ASM Failure Groups and Disk Controllers

Hey guys,
I understand that it's considered a good idea to set different Failure Groups for disks which could fail at the same time because they share hardware, For example, disks that share the same disk controller.
Now, my question might be silly but I don't understand why we would configure multiple disks with the same disk controller.
Thank you,
Jerry.

Jerry wrote:
Hey guys,
I understand that it's considered a good idea to set different Failure Groups for disks which could fail at the same time because they share hardware, For example, disks that share the same disk controller.
Now, my question might be silly but I don't understand why we would configure multiple disks with the same disk controller.
Hi Jerry,
Your question is not silly.
Usually you have one or more disk controllers in a system
Each controller can handle up to x disks ( in the past this was 15, don't know if this still is )
If you wanted to be redundant, like with RAID1 ( mirrorring ) configurations a system was usually configured to have an even amount of disks
spread evenly over two controllers.
This then covered disk-failure and controller failure, as each logical disk in the mirror-set is accessible over two controllers and consists of -at least - two disks.
In ASM you would configure the main diskgroup on the first set of disks on the first controller.
The failure group would then be configured on the second set of disks on the second controller.
In the SAN world, with ASM using Host Based Mirroring, the Failure group can also be a diskset on a totally different storage-server
Edit: Totally forgot: More disks on one controller mean more parallel access to your data, as you can read all seperate disk seperately.
In the current days with the enormous disks it is quite easy to configure just one disk in your system, but that will bring you quite easy huge performance problems
HTH
FJFranken
Edited by: fjfranken on 20-jul-2011 6:53

Similar Messages

ASM Failure Groups

Hello everyone,
on 10204,
currently my database uses ASM & is of externel redundancy.
I've to mirror the entire set of disks to another set of disks.
I'm planning to use ASM failure groups for that.
can anybody provide useful links for that feature. Can't get much idea from oracle doc
thanks

Hi;
How To Add Back An ASM Disk or Failgroup (Normal or High Redundancy) After A Transient Failure Occurred (On Release 10.2. or 10.1)? [ID 946213.1]
ASM Technical Best Practices [ID 265633.1]
Also see:
Master Note for Automatic Storage Management (ASM) [ID 1187723.1]
ASM Management
http://www.oracle-base.com/articles/10g/AutomaticStorageManagement10g.php
Regard
Helios

Create ASM Failure Group via dbca

I am not sure how to configure a Failure Group in ASM.
I am not using asmlib.
So I start dbca - choose configure ASM
Create Diskgroup --> Data
select my 2 raw devices ( which are on 2 storages)
I select normal redundancy;
Disk Path ASM Name Failure Group
/dev/raw/raw4 Data1 FG1_Data
/dev/raw/raw5 Data2 FG2_Data
Is this enough ? Or is there anything else needed for a functional failure group ?
Does that mean, when one storage (with disk Data2) is switched off - that my instance will survive and is still able to write data on the diskgroup ?

Hi,
What is your oracle version?

How to define ASM failure groups!

Hi all,
I have 4 disk on both disk controller
SATA controller
ASMDISKO1
ASMDISKP1
SCSI controller
ASMDISKR1
ASMDISKS1
I created diskgroup test as below:
CREATE DISKGROUP TEST EXTERNAL REDUNDANCY
FAILGROUP controller1 DISK 'ORCL:ASMDISKO1', 'ORCL:ASMDISKP1',
FAILGROUP controller2 DISK 'ORCL:ASMDISKR1', 'ORCL:ASMDISKS1';
but i got this error:
ERROR at line 2:
ORA-15106: missing or invalid operating system disk locator string
Please help!
Thank you!

What does controller1 means and where can i find it? do i need to put in the create diskgroup like the example? its a failgroup name since we're creating DG with normal redundancy, after creating it you can find detail on this from v$asm_disk
see below example.
creating diskgroup with NORMAL REDUNDANCY with 2 disk (68gb each)
CREATE DISKGROUP TEST NORMAL REDUNDANCY
FAILGROUP controller1 DISK
    '/dev/rhdiskpower8'
   FAILGROUP controller2 DISK
'/dev/rhdiskpower9' ;
ASMCMD> lsdg
State    Type    Rebal Unbal Sector Block       AU Total_MB Free_MB Req_mir_free_MB *Usable_file_MB* Offline_disks Name
MOUNTED NORMAL N      N         512   4096 1048576    139424   139322                0           69661              0 TEST/
ASMCMD>
SQL> select GROUP_NUMBER ,NAME from v$asm_diskgroup;
GROUP_NUMBER NAME
           5 TEST
SQL> select GROUP_NUMBER,FAILGROUP,label ,path from v$asm_disk;
GROUP_NUMBER FAILGROUP                      LABEL                           PATH
           5 CONTROLLER1                                                    /dev/rhdiskpower8
           5 CONTROLLER2                                                    /dev/rhdiskpower9Please close the thread if you feel you have the answer and keep the Oracle forum clean.
https://forums.oracle.com/forums/ann.jspa?annID=885
Thanks
Kuljeet Pal Singh

ASM - Service Guard/SGeRAC - Disk Groups - Sizing

Hai.
I'm new to ASM. We want to use ASM with HP-UX11.23 and MC Service Guard/SGeRAC A11.1.17. We decided to start with initial DB sizing of 25GB, I mean the Disk Group ( hence, Volume Group) size. So, I would like to know recomended no: of Disks in this Disk Group and Disks sizing? We want to go with only one Disk Group. Also, I have few questions:
1) Do we need to have separate Disk Groups for ArchiveLogs & Database Files?
2) Can we use ASM Disk Groups for Archive Logs or is a regular File System recomended or can we have both?
regards,
Dileep Tallam.

Looking at the scalability and Data Growth data rate in you Org.., say in next 2 to 5 years ..... Estimate the size of Disk Group.
Single Disk Group is a good idea, as multiple disk groups gives no performance agains.
If planning for Flash too , Then give a separate Disk Group to Flash.
Comming to
1) Do we need to have separate Disk Groups for ArchiveLogs & Database Files?
No need for a separate Disk group for Arch/, Ctrl, Data, Redo. You can put all in one Disk Group.
2) Can we use ASM Disk Groups for Archive Logs or is a regular File System recomended or can we have both?
Archive Logs are supported on ASM. Depending upon your Backup Stragey.
If RMAN - ASM
else
file system.
Regards
Satish

What is the failure group in ASM and the meaning of ASM assigns each disk

Hi
Please help me in understanding
what is the failure group in ASM and the meaning of "ASM assigns each disk to it's own failure group, by default"

As you may have known ASM uses mirroring and striping of files. Mirroring is storing same compies/parts of files in different disks/controllers. When creating disk group which could consist of several disks, you have to assign disks at least to separate failure groups for normal redundancy , or three failure groups for High redundancy. This means that ASM will never assign mirrode copies/pieces of files to the same failure group. So, assigning disks to different failure groups you make sure mirrored copies are not on the same physical storage. Saying with other words, failure group gives your more abstract meaning based on which you can organize your physical disks contained in disk group.
That is why for normal redundancy at least two failure groups are needed, because there are one mirrored copy of each extent(allocation unit, to be exact) and for high redundancy the requirement is at least 3 failure groups, because each allocation unit has 2 mirrored copies, which should be on different failure group, consequently.
Hope, this explanation is helpful.

Creating diskgroups and failure groups on windows

Hi,
I have a Windows 32-bit with two drives of C: and F:. I have an Oracle database that I like to migrate to ASM. I ran the utility localconfig.bat with the add option which successfully started CSS services and installed ASM and started it up.
In DBCA I tried to create diskgroups but there is no way to do it. How can I create diskgroups and failure groups on windows?

You have to use the ASMTOOLG (or asmtool) program to "mark" the disks for use with ASM. Once done, DBCA should recognize the disks.
You might check out Julian Dykes powerpoint on installing RAC and ASM on Windows for more helpful info.
Cheers!
Jay Caviness
http://www.grumpy-dba.com

RAC and ASM with geographically seperated disks

We are planning to use RAC and ASM with four nodes. The two nodes will be at one location and another two nodes at different location. The ASM disks also will be available locally. Is it possible to configure ASM with geographycally serepared disks.
We are thinking of two RAC and ASM setups with two nodes each and streams replication between the RACs.
I want to know what is the best method to implement. Is it RAC with four nodes OR two RACs with two nodes each and streams replication between the RACs.

Apart from the latency issue, which has been mentioned by others, you also need to mirror your disks between the two sites and be very careful about split brain scenarios under node or site crashes.
You need to mirror the disks between the sites in case one site crashes completely and loses all network access. The only way the second site can carry on is if it has access to all the data disks, and the cluster control disks (terms vary for this, such as quorum or voting disk). If you do not mirror you simply do not have a resilient design. Resilience is about eliminating all single points of failures, which means duplicating everything i.e. mirroring.
And mirroring between two remote sites adds more volume to the data traffic between the two sites. And it would need to be synchronous rather than asynchronous to guarantee no data loss. And your commits for each transaction would be limited by the round trip time to write to the remote site and get the acknowledgement back.
Split brain is something you need to avoid with remote clusters, and local clusters too. If the network goes down between the two sites and both sites have local copies of all of the data and cluster control disks, which site becomes the primary and which one becomes the standby? You cannot have both sites coming back up as primary with active databases and accepting transactions! At this point you have split brain, and each side is processing transactions independently, and both databases are now deviating from each other with different data changes.
I don't think a 4 node RAC environment split across geographical distances is really viable, except under small transaction volumes, and where response time (transaction time) is not critical. If you have high volumes and need fast transactions then you need to only use local RAC configurations, and replicate between the two sites asynchronously. DataGuard is easier, but you need to decide if you need Streams and how to make it work for you.
John

What exactly is a failure group?

Oracle Version : 10GR2
2 node RAC running on Solaris
I am trying to understand what a failure group is. Googling didn't help much .
If i want to store 1 TB of data and needs it be to proteced either by NORMAL or HIGH redundancy and i have 3 slices of 1TB each available like
/dev/rdsk/c4ikdzs1
/dev/rdsk/c4ikdzs2
/dev/rdsk/c4ikdzs3How does a failure group come into picture?

In your example, you would not need the concept of failure groups. But let's assume you had 4 disks on two different controllers like:
c0t0d0
c0t0d1
c1t0d0
c1t0d1
And you want to set up a diskgroup with normal redundancy on these 4 disks. In that case, wouldn't it be useful to let ASM know that two disks share the same controller and wouldn't it be nice if ASM was able to mirror data on disks across both controllers (like mirroring between c0t0d0 and c1t0d0 instead of c0t0d0 and c0t0d1) so that you still have an available pair of disks even if one controller fails.
And that is what failure groups are for.

Requirement to have all Failure Groups of equal sizes

ASM user guide states the following:
"Failure groups should all be of the same size. Failure groups of different sizes may lead to reduced availability."
Let's say we have four FGs in a disk group with Normal Redundancy: 2 x 1TB + 2 x 2TB.
Does this config still create a possibility of "reduced availability"? Or will ASM place two copies of each block in the larger FGs even after the smaller FGs are out of space, so that redundancy is maintained?

Hi,
Let's say we have four FGs in a disk group with Normal Redundancy: 2 x 1TB + 2 x 2TB.
Does this config still create a possibility of "reduced availability"? Or will ASM place two copies of each block in the larger FGs even after the smaller FGs are out of space, so that redundancy is maintained?
Failgroup is logical entity of a diskgroup which consist of disks .
You should have same sized disks on all failgroup of a diskgroup.
Because ,ASM places mirroring extent on a disk of other failgroup depending on partnership of disks .
And while creating partnership it will not check disk size at OS level.
So,they will keep populating and reach maximum size of the disks while other disks might have space .
Then new files will run into reduced redundancy in future .
To enforce this in future release ,We are going to check disk size while adding into a diskgroup ,if adding disk is not of same size ,then it will fail.
same for creating diskgroup ...
Regards,
Aritra

ORA-15072: command requires at least 2 regular failure groups, discovered only 1

Hi,
I'm trying to create a diskgroup for a temporary purpose. I didnt mention the type of redundancy. When i ran the below command i got the mentioned errors.
SQL> Create diskgroup temp_dg disk '/dev/mapper/003w1_e2p5' attribute 'compatible.asm' = '11.2.0.0.0';
Create diskgroup temp_dg disk '/dev/mapper/003w1_e2p5' attribute 'compatible.asm' = '11.2.0.0.0'
ERROR at line 1:
ORA-15018: diskgroup cannot be created
ORA-15072: command requires at least 2 regular failure groups, discovered only 1
When i used two disks, then diskgroup got created.
All the diskgroups in ASM are of EXTERNAL redundancy.
SQL> Select distinct type from v$asm_diskgroup;
TYPE
EXTERN
I would like to know why it was asking to create diskgroup of NORMAL redundancy. Is there some thing like default REDUNDANCY in ASM.
Please share your views.
By,
Step Into Oracle DBA

Hi,
When i used two disks, then diskgroup got created.
Becuase default redundancy for create diskgroup is NORMAL.
SQL> Select distinct type from v$asm_diskgroup;
TYPE
EXTERN
Did you sure your diskgroup is created?
Mahir

How Do I Group Multiple Disks as One Album?

I've got the latest iTunes update, 11.0.4, and as with the update before it, I'm supposed to be able to group multiple disks as one album, but I can't figure out how, and can't find any directions at Apple.
I've lately begun ripping my large collection of symphonies and operas on CD into iTunes. Operas especially almost always come on two, three, or even four CD's, BUT IT'S ALL THE SAME OPERA, and the CD's come in the same boxed set. On top of that, there really aren't any "tracks" in an opera; the plot and the music unroll seamlessly from beginning to end (that sometimes takes 5 or 6 hours, which goes with the operatic territory).
On my CD player, I'm used to a pause between disks, but now that I've figured out how to get the "tracks" on each CD to play in order on iTunes (not so intuitive), I'd like to be able to go from the last "track" on Disk 1 to the first track on Disk 2 without interruption, since the technology should be able to support that option.
In the INFO box, I've tried keeping "1 of 3," "2 of 3," "3 of 3." No joy. So I've tried erasing the first element, 1, 2, 3, and just leaving the total number of disks. Again, no joy.
Since the album name is often filled in with something like "Carmen [Disk 1]" for example, and since Albums should have exactly the same name so that iTunes can figure out that in fact, they belong to the same work, I've tried deleting '[Disk 1]" etc. on all 3, leaving just "Carmen" in the appropriate space on the INFO panel for each of the 3 disks. Doesn't work.
Has anyone else been afflicted with the same problem?
Has anyone got a solution?

Have you seen this helpful article:
Grouping tracks into albums:
http://samsoft.org.uk/iTunes/grouping.asp
In the INFO box, I've tried keeping "1 of 3," "2 of 3," "3 of 3."
That is correct. Don't erase the first element, 1, 2, 3, that should not matter.
Since the album name is often filled in with something like "Carmen [Disk 1]" for example, and since Albums should have exactly the same name so that iTunes can figure out that in fact, they belong to the same work, I've tried deleting '[Disk 1]" etc. on all 3, leaving just "Carmen" in the appropriate space on the INFO panel for each of the 3 disks.
Also correct. Also chec, if the "Sort album name" is the same.
Do the artists differ on the tracks?
Then set the "Album Artist" on all CDs to the same name (Various Artists), also check, if the album sort artists names differ.

New Mac with major permission and disk-write problems

Right, so I'm pretty new to Mac, after getting my first Mac computer (a 17-inch MacBook Pro) at the end of January this year. It's been great so far and I love the thing, but I've suddenly encountered some crazy problems which I'm pulling my hair out over because I have tried everything to fix them, and have had no luck.
I'll try to include as many details as possible, and I'm prepared to bear with anyone who asks me about something I've alrady tried, just so I can get this sorted.
Okay, so first of all, the main problem seems to be with permissions, mostly with disk-write permissions. Any apps that I want to install that required keychain access will no longer install. I enter my keychain password, hit Return, and the dialog box closes without continuing. So I hit "Install" again and it becomes a never-ending cycle of entering my password to no avail. Now, this happens with ANY application that requires keychain access to install. It is not limited to any particular application. I know my password is right because the box closes, and if I enter it wrong, the dialog box shakes because it is incorrect.
Furthermore, it seems keychain access is problematic in other apps. If I want to authenticate something, it will do the same thing as I mentioned before, meaning I get nowhere with the application.
From here, it gets worse. If I download something (anything), then restart my computer, it is still there. As it should be. However, if I delete an APPLICATION (not just any file) OR change preferences for some programs (one in particular that I specifically don't want starting up on.... startup), including through System Preferences>Users & Groups>Login Items, they will not save. This is driving me insane. For instance, I downloaded some free apps from the Mac App Store to try out, but decided I didn't want them. I tried to deleted them from the app folder and succeeded. Emptied trash. Gone. Restart, and.... they're back? So I tried to uninstall them via the Mac App Store, once I found you could do that. Again, it didn't work. Any Login Items preference changes don't stay after a restart.
Originally, none of this was a problem and everything was working fine. The first sign that something was wrong would be Apple Mail often asking for passwords, usually for my Hotmail accounts, saying that they were rejected by the server (but are correct passwords, I get the emails from the accounts, and the passwords are always accepted once I type them in, only to be asked for them some time later on for no apparent reason). At the time, I tried to repair the keychain, tried deleting and recreating the mail account entries and what not, but nothing helped. It still happens, but at the time, it was more of a niggly thing than an outright problem.
I should also mention that I did use BootCamp to install Windows 8 on a small partition, but after I couldn't boot back into Mac (I didn't realise you had to use the Option key whilst booting), I found out that you had to hold the Option key to get back into Mac, then used BootCamp to get rid of Windows. Everything was fine so far. Until I decided to reinstall Windows 8 with BootCamp. This is where things started going wrong. I decided to install a bootloader to make it easier for me to boot between the two systems. I was tossing up between rEFIt and Chameleon, and decided that rEFIt would be the best for my needs. So I downloaded and installed it, which seemed to go fine. Until I restarted. Mac would endlessly load (the spinning grey dots with the Apple logo).
Now, I actually managed to fix this, but I should probably go into more detail. First of all, holding the option key and selecting my Mac partition would allow me back into Mac, and same with Windows 8. At this point, I decided to uninstall Windows 8 to try fix my problems, except now BootCamp was giving me errors. I believe it was something about being unable to unmount the disc, but it may have been a different error. I don't entirely remember. So then I decided to try getting rid of rEFIt. I followed the instructions on the official site but it didn't work. So then I tried deleting the files with root (sudo) access through terminal. Which also failed....
So to the Recovery partition. Booting into Disk Utilities, I repaired permissions, which worked fine, and repaired the disk. I believe I had run the disk repair a few times before to try to fix BootCamp when it stopped working. Anywaym it had worked before, but this time, it said that it was corrupted and could not be repaired. Something about needing to reinstall Mac OS X. With all my files on this computer and currently nothing to back it up with (eventually I will have something to do backups with, but it'll have to wait a few months), I'm not going to do that.
Finally, I managed to delete the rEFIt files through Terminal within the Recovery partition. I ran permission repair and disk repair again to clean anything up. Disk repair gave me the same error, but now I could get back into Mac without holding the option key on every **** boot.
Now more problems had presented themselves. I decided that the lock under Login Items was probably preventing me form successfully changing my startup items. Trying to unlock it did the same thing as I previously mentioned. Type in my password, keychain accepts it, then nothing happens. The keychain settings were already defaulted so that keychain would stay unlocked after authenticated, and all stuff like that. Using "Get Info" on anything has permissions locked and again, I cannot unlock to change them, although looking at a PDF file just now, whilst still locked, it would allow me to add or remove users, so maybe that's not completely accurate. I believe I tended to look at the system folders though, and my name wasn't under ownership, although I don't believe it was meant to be, but I was hoping that maybe that would fix the problem. I guess not.
At this time, I still had my Windows 8 partition sitting around and couldn't get rid of it. I heard of the manual way to do it through Disk Utility. I tried this in Mac OS X, and through the Recovery partition, but neither worked. An error about being unable to unmount the drive. I finally found a way to remove it. Honestly, I don't completely remember how I did it, but I believe it was through a command line, uh.... command. Now I had free space that I couldn't use to expand my Macintosh HD partition back to full size, again with the unable to unmount error. Finally, I fixed this by booting from a Mac OS X installation disc that I happened to have, and using Disk Utility off of that. After that, Disk Utility no longer gave me errors for disk repair.
However, my other problems all still remained. I had written a little list of things I found on the internet for fixing my problems. One solution was to use "resetpassword" through terminal under the Recovery partition, then select Macintosh HD and select "Reset Home Directory Permissions and ACLs". That didn't work until I tried it through the Disk Utility on the Mac OS X installation disc. That worked, and once I was back into Mac, Spotlight started indexing again. However, nothing else had happened.
I should also mention that keychain access isn't completely non-existent for me. Setting up a new WiFi connection worked for me (that is, connecting to a new network), but now every time I connect to the network, I have to authenticate it. However, it does accept my keychain password and eventually connect.
Now, another thing on my list to try was single-user mode, and using "/sbin/fsck -fy" until everything was okay. Well, the first time, it found a bunch of errors, then fixed itself up. Then it was all okay. But nothing had changed. So trying again, I this time used ?/sbin/mount -uw /" which I believe is meant to allow writing access to the drive. Now when running "/sbin/fsck -fy", I had an error. Specifically, "Journal need to be replayed but volume is read-only".
So that's pretty much where I am up to at the moment. It seems to be a poblem with write permissions, possibly among other things. If it was Windows, I might be able to work it out easier, but being new to Mac, I'm still finding my way around. I guess this is a good learning experience, but it's not fun to have to deal with it so early on.
If anyone can help me, I'd greatly appreciate it. I have tried many things, so if you suggest something that I have tried and possibly forgot to mention, I'll let you know, but any help is still helpful, even if only eliminating possible problems/causes/solutions.

Actually you first post is so long that most people just glance at it and move on. To say the least you are very verbose.
Your problem stems from something going wrong with permissions, as you know. How and why that happen is usually a user error of some type.
You can try to repair permissions and see if that corrects it. If not I will leave other options to someone that may know more about the permission system on a Mac.

AP groups and redundancy

Is it possible for APs to failover between controllers when AP groups are in use? I have seen separate documentation on AP groups and AP failover but nothing that says how to implement both at the same time.
I have tried to work it out but when I created the group on the back up controller I am not able to add the AP to the group as it is not asociated to it.
Has anyone else come across this or have any ideas?
We are currently using 4400 controllers running 5.2.

Are your controllers in the same mobility group? (Controller|General|Default Mobility Name)
You can also check under Controller|Mobility Management|Mobility Groups to see if other controllers are set up to exchange Mobility Management info.
If you are in the same Mobility Management group then when failover to another member/controller in that group occurs and the AP Group name is the same on both controllers the APs should automatically join that AP Group name on the controller they failed over to.
Our implementation (still in the early stages) includes 8 WiSMs Controllers that are in the same Mobility Management group and will fail across campuses if we lose a WiSM module or chassis.
We will be using smaller controllers (4402's) at remote sites with their own Mobility Name. That is to prevent constantly exchanging client info with other controllers over wan links. If/when those failover to the main campus they will wind up being in the AP Group default-group on the WiSM environment.

WiSM redundancy, mobility groups and RF groups

Hi there
we would like to implement the following:
- Support for about 2000 LAP's
- 1 x Catalyst 6509
- 1 x Sup 720
- 7 x WiSM's
What I'm interesting is are the following points:
1. I thought that we would build the switch completly redudant, so we have to wlan switches (switch A and B) with 7 WiSM's eatch. So I can garanty a N+N redundancy --> each LAP's has a primary controller on switch A and it's secondary controller on switch B. The LAP's can be splitted on the two switches, but for your understanding there is a 1:1 redundancy. What do you think of this design, is the too much or is this appropriate?
2. As I know you can build up a mobility group of a maximum of 24 controllers or 12 WiSM's. I would put only these controllers in a mobility group, where Layer 2 roaming can occure.
3. But what is about the RF groups - there is a maximum of 1000 LAP's, so I can put only 3 WiSM's in one group. But this would not work form me, then I would have 2 WiSM's on switch A and only 1 WiSM on switch B in a RF group (not a 1:1 redundancy). First is it possible to put WiSM-A and WiSM-B into different RF groups, I think so because they are logically splitted, aren't they?
And what RF group design would be best (just as a reference)? I thought that it would make sense to form a RF group for each of the seven pairs (1 WiSM on switch A and 1 WiSM on switch B) for redundancy? What do you think of that approach?
4. So I would have 1 mobility group and 7 RF groups. Or do you recommend to form the mobility groups like the RF groups? But what happens with Layer 2 roaming in that case?
I'm sorry for the long and messy text, but I hope you can see my design questions?
Thanks a lot in advance.
Dominic

It sounds like you already have some good replies. Personally I like N+1 redundancy, but that is a designers choice. One thing I should point out is that the 6500 can only support 5 WiSM cards each. In this case a 4 WiSM x 3 chassis option would give your more spare capacity with only 12 total cards. The lower WiSM cost (12 vs 14) would help offset the cost of the extra chassis. You could also support 2400 APs with 8 WiSM cards even if one switch is down.
Not too long ago Cisco added the ability to set the priority of APs so your critical ones would join a controller and the less critical ones would go down if a controller failed and there were no redundancy. That is something to keep in mind when designing wireless. You may not need redundancy for all APs and that could affect your design and costs.
Randy

ASM Failure Groups and Disk Controllers

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