Hot spare and identifying volumes to drives.

I have a fully populated Xserve RAID with 500GB drives. I set each side up to use 6 of the drives in RAID5. I left one drive to be used as a hot spare for each side. Now, how does that work if a drive from a RAID goes south? Will the controllor automaticly start rebuilding the data on that drive? How does the controller know to use the drive? I haven't touched the drive in the RAID admin at all.
Second question. I have a second Xserve RAID with two 250GB drives on each controller. Not thinking I set up the two drives one each side as RAID0 at the same time. Of course I need to be able to identify which volumes belong to which set of disks. Is there a way to do this with disk utility? I really don't want to have to reformat these things just to identify which is which. Thanks.

David,
Hot spare use is automatic. Any drive not part of a RAID set is automatially used as a hot spare. So if a drive fails, the RAID set will start being built on the hot spare immediately.
On the second question... how about just disconnecting one of the fibre cables, then you'll know with 100% certainty which one you're formatting. Once you've done that, you can reconnect the second side and format it. Simple, but it will work

Similar Messages

Raid- Understanding "Hot Spare" and Windows reinstall - Final Steps

Hello all,
If you follow couple of my other recent threads here you will see I have a warning of a failing drive in my 4 tb raid (4 x 1TB raid set.)
Also for an unrelated reason I am also needing to reinstall Windows 7. (and of course my Adobe Master collection CS5)
I ordered a 5th drive to serve as "Hot Spare" and it will be arriving sometime today from Amazon.
I want to make sure I do the above "final steps" properly, in the correct order.
I am basing my "final steps" based on Harm's advice on another thread:
>>>
You can never be too safe with data, but if you follow the hot-spare, extend raid set and rebuild sequence, it is not necessary. Your data will be reconsructed automatically. That is the reason you use a raid3/5.
Your log file is a definite show of a serious disk problem. Replace it, create a hot-spare, extend your raid set and rebuild (it should be done automatically) and you are ready to roll
>>>>
(As a precaution I have done a backup of my raid, to an external drive)
So once my new hard drive arrives today from Amazon, I will, in the following order:
1) Replace failing hard drive. (Do I need to power down the computer to remove the failing hard drive and replace it with the hot spare? Or can I leave the computer powered on so that the raid software can continue its CONSISTANCY CHECK while II do all of the steps to rebuild the raid --- see note at bottom of this post...)
2) Create hot-spare
3) Use the Raid controller software (Areca) to EXTEND HOT SPARE
4) Rebuild raid (it should be done automatically)
THEN, after I confirm that the raid is working okay, I will
5) Reinstall Windows 7.
THe below step is what I am not entirely clear on:
6) I assume since the raid has already been rebuilt {before I did the windows 7 reinstall) I can do a very straightforward "reconnect" to the already working raid. In other words, I would reinstall the Areca raid software (using the Areca cd) and identify the raid and windows 7 will recognize the 4 tb raid as my raid drive.
I am tracking the delivery of my new hard drive and it is at least 5 or 6 hours away from arriving from Amazon.
**** CONSISTANCY NOTE: I the meantime I am having the Areca web based controller software do a CONSISTANCY check of the raid.
It is half way through the check and has found 144 errors so far. The consistancy check is rather vague about what it is doing. But can I assume that it is finding the errors and will automatically fix them.
Or do I have to do something to fix the errors once the consistancy check is finished (This is one reason why I would like to avoid powering down during the rebuilding of the raid.) Or will creating the hot spare, etc interrupt the consistancy check, meaning I must finish the consistancy check completley before rebuilding the raid.
Or should I abort the consistancy check and do that after I reinstall windows. (If possible I would like to do that so I can get on with the editing of my current project!!)
WHEW!
Rowby
Message was edited by: rowby

WEB BROWSER-BASED CONFIGURATION
132
6.6.5 Check Volume Set
To check a volume set from a RAID set:
(1). Click on the “Check Volume Set” link.
(2). Click on the volume set from the list that you wish to check.
Tick on “Confirm The Operation” and click on the “Submit” button.
Use this option to verify the correctness of the redundant data in
a volume set. For example, in a system with dedicated parity, volume
set check means computing the parity of the data disk drives
and comparing the results to the contents of the dedicated parity
disk drive. The checking percentage can also be viewed by clicking
on “RAID Set Hierarchy” in the main menu.
Directly from the Areca 1600 series Manual. I would let that finish.
Eric
ADK

Question Regarding Hot Spares and Submirrors

I'm currently running a V210 with mirroring implemented on two disks. Is it possible for a submirror to also be a hot spare? In other words if I have a mirror (d0), can d1 or d2 (each being a submirror of d0) be configured as a hot spare?
Thanks.

Should you attempt to do that, I'm certain you will find your answer being no.

300 GB disk as hot spare for 146 gb disk in stk 6140

Hi,
Does any body know this for sure?
Customer plans to buy new tray with 300 gb fc disks.
Also hey have old tray with 146 gb disks.
They want to assign two 300 gb disks as hot spares for old 146 gb and for new 300gb disks.
Will it work?
If you can confirm that this works, does this depends on firmware revision or CAM version or something else?
Thanks in advance!

I have not seen this work but It's my understanding that hot spares are "array spares" and that a larger drive can be a spare for a smaller drive.
Glen

Mirrors & Hot Spares

Relativley new to Solaris 10.
I have 5 identical disks (75GB) on my system and I have the following setup:
disk1: /
disk2: /data
disk1 is mirrored to disk3, disk2 is mirrored to disk4. I managed to get the mirroring done first time, however what I would like to do is have some sort of automated process to have the 5th disk (disk5) substitute in for any other disk that fails.
I guess it is something to do with Hot Spare Pools but I am not sure where to start with it.
I did all the mirroring with command line tools (metainit, metattach, etc...).
If anyone can please point me in the right direction that would be appreciated.

This may seem a silly question but have you checked the Sun online docs at:
<http://docs.sun.com/app/docs/doc/816-4520/6manpielm?a=view>
which seem to pretty good at describing how to set up the hot spares and then associate them with slices.
cheers

When to replace drives, and when does the hot-spare kick in?

Here's the situation: got an e-mail today from the RAID (no it wasn't a love letter), which alerted me to a ten-times repeated ERROR: 0x10, STATUS: 0x51 on drive 8
I then proceded to check through the log, and found from a while back (mysteriously I never received an e-mail even though it said it had sent one!) ERROR: 0x40, STATUS: 0x51
which were however only single/double incidents, not repeated 10 times like this latest error.
Despite these errors, the drives show up as "OK" in RAID Admin, and the hot spare drives seem not to have been activated.
The question is now, should I get these drives replaced ASAP, or if the RAID lists the drives as OK is everything fine and dandy? (not sure how to take a "non-recoverable error 0x40" and reconcile that with a drive status of OK)
Ronald

Nobody's got any answers? Bummer! The Apple manual says really nothing useful about how to aAsSsSeEsSsS error messages and when to replace drives, etc.
It's nice to sell to people that a RAID-5 will keep the data safe, but that only works if one knows what to make of the error messages.
I shouldn't have to spend another $1k for a tech support contract, just to learn what things mean that should be explained in the tech docs...
Ronald
PS: will someone tell Apple's PC watchdog that aAsSsSeEsSsS has nothing to do with aAsSsS? AaSsSsEeSsSsMmEeNnTt is a technical term, yet it wouldn't want to let me post the message because it contained aAsSsSeEsSsS! What's next? Soon we can't use the word RAID anymore, because it's refers to undesirable violence...
Someone please pick up a dictionary, in Tiger there's both a regular app and a widget to do so, so it shouldn't be that hard...

Replace the Hot Spare that Shared between Raid 1 and raid 5

I have ProLiant ML370 G6 with Smart Array P410i Controller on System Board
I have two Logical Drive (Logical Drive 1 - Mirroring (RAID 1) And (Logical Drive 2 - Distributed Data Guarding (RAID 5)
The logical Drive 1- Mirroring (RAID 1) Have two Physical Drives
The Logical Drive 2 Distributed Data Guarding (RAID 5 Have three Physical Drives
And There Are One Spare Drive Shared btween RAID 1 and Raid 5
Controller Configuration Summary
2 Data Array(s)
2 Data Logical Drive(s)
5 Data Drive(s)
1 Spare Drive(s)
The problem :
there are that the spare Drive FAil and have warining To replace it
I replace this drive with new one but the repulid for the Drive not start and Give Inactive
How Repulid the Hot Spare drive ?

Hello Amostafa,
Welcome to the HP Forums, I hope you enjoy your experience! To help you get the most out of the HP Forums I would like to direct your attention to the HP Forums Guide First Time Here? Learn How to Post and More.
I understand that you are looking to rebuild the hot spare drive on your ProLiant system, and I would be happy to guide you towards a resolution!
I am sorry, but to get your issue more exposure, I would suggest posting it in the commercial forums, since this is a commercial product. You can do this at:
http://h30499.www3.hp.com/t5/ProLiant-Servers-ML-DL-SL/bd-p/itrc-264
I hope this helps!
Regards
MechPilot
I work on behalf of HP
Please click “Accept as Solution ” if you feel my post solved your issue, it will help others find the solution.
Click the “Kudos, Thumbs Up" on the right to say “Thanks” for helping!

Sun StorageTek 5320C NAS, SNMP and hot spare

Hello,
We have 5320 NAS cluster system, and one Controller Unit with 16 FC 300 GB hard drives. Drives are as follows:
from 1 to 8 hard drive -> RAID5
from 9 to 15 had drive -> RAID5
16 hard drive -> Global hot spare
SNMP query for hard disk status:
$ snmpwalk -O n -v 2c -m "/home/nierka/st5320c_.mib" -c <comunity_not_shown> <IP_not_shown> st5320CRaidPhysicalDriveStatus
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.2 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.3 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.4 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.5 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.6 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.7 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.8 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.9 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.10 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.11 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.12 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.13 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.14 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.15 = INTEGER: online(4)
.1.3.6.1.4.1.42.2.28.13.3.16.1.2.3.4.1.3.1.2.16 = INTEGER: online(4)
$
Where is hot spare status "stand by(5)"? Using "raidctl" command we get these lines:
head1 > raidctl get type=lsi target=profile ctlr=0
........<cut>...........
Total hot spare drives: 1
Standby: 1
In use: 0
........<cut>...........
Why SNMP can't get hot spare status? Where to report this issue? Thanks in advice.
Nerijus

Thanks.
To answer your question, the disk FW upgrade doesn't erase/destroy the data. However the disk FW upgrade can ONLY be done while there is NO IO activity, hence you need to stop the IO before proceeding with such upgrade.
As for the FW, it seems that your drive has the FW 0892 which is a newer FW than what your CAM version has (0791). The FW 0891 was supported with CAM 6.0 + patches. Starting from CAM 6.1.0_15 we introduced the FW 0B92.
The recommendation is to upgrade CAM to 6.4.1, then you will get an alarm because your drive will have 0892 whereas CAM brings 0B92, however you can plan a maintenance window at your convenience in order to upgrade the drive FW.
Regards
Nicolas

"$RECYCLE.BIN" and "System Volume Information" on a hard drive connected to EA4500

Hello
I've bought WD Elements 3 TB USB 2.0 External HD WDBAAU0030HBK hard drive for my Linksys EA4500. The hard drive was NTFS formatted. After I plugged it in I see "$RECYCLE.BIN" and "System Volume Information" folders on it via my Windows Explorer. I know these folders to be Windows system folders, but my hard drive is now connected to router. So do I really need them, or can I safely remove them?
Solved!
Go to Solution.

The EA4500 does not have to anything with these folders popping-up since they appear on the computer by its design- system file and cannot be deleted permanently. I had read some notes on how to hide these files; you can try these if you want:
It works as a part of recycle bin in your desktop. To make this disappear, go to Tools > Folder Options > View and uncheck “Hide protected operating system files”. System Volume Information is where windows system restore files are located. If you do not want to use this folder then disable System Restore.
But just to be safe, leave it as is. This should not make any issues or problems in accessing the files from the HD using the computers connected to the EA4500.

DB identifier mismatch with data volujme and log volume

Hi,
I would like to perform backup and restore test on linux (maxdb database ) ECC 6.0 system.
I have taken the backup of (i.e data , incremental and log backups ) on one system.
Then created a new system with same host name, SID and instance number.
Then i Performed to restore the database on the new system in the ADMIN mode.
First i done the data then incremental backup. These are successful on the new system.
But when i performed the log backup it gives the following error as :
Db identifier mismatches with data volume and log volume.
Database then goes to offline state.
How to perform the successful log backup ?
Thanks
Srikanth

Hi,
As you are performing restore on the new machine you have to restore with recovery with initialization option.
for this you have to first create template on the new machine using DBMGUI or DBMCLI for complete_bkp/incremental_bkp and log_bkp's.
It will first restore complete backup after that incremental backup and after that all the available log backups will be applied.After that you will be able to make in online mode.
You can perform this either using dbmgui or dbmcli.
http://help.sap.com/saphelp_nw04/helpdata/en/d1/b386654dc211d4aa1100a0c9430730/frameset.htm
Regards,
Sahil

Why is hot spare in use while disk state is Okay

In my Solaris 10 RAID-5 volume, metastat shows the hot spare in use, but all the disks' state is Okay. Why is this? I do suspect the first disk was bad at one time, and may have been pulled out and re-inserted in without issuing any solaris commands. Please help explain why, and how to recover from this situation. Thanks.
d10: RAID
State: Okay
Hot spare pool: hsp000
Interlace: 32 blocks
Size: 860024640 blocks (410 GB)
Original device:
Size: 860032704 blocks (410 GB)
Device Start Block Dbase State Reloc Hot Spare
/dev/dsk/c10t500000E01013A380d0s2 10506 No Okay Yes /dev/dsk/c10t20000004CFAA17C8d0s2
/dev/dsk/c10t500000E01013A230d0s2 10506 No Okay Yes
/dev/dsk/c10t500000E01012D7A0d0s2 10506 No Okay Yes
/dev/dsk/c10t500000E010128CE0d0s2 10506 No Okay Yes
/dev/dsk/c10t20000004CFC22131d0s2 10506 No Okay Yes
/dev/dsk/c10t500000E01012D7B0d0s2 10506 No Okay Yes
/dev/dsk/c10t20000004CFAF377Fd0s2 10506 No Okay Yes
hsp000: 1 hot spare
Device Status Length Reloc
/dev/dsk/c10t20000004CFAA17C8d0s2 In use 143349312 blocks Yes
Device Relocation Information:
Device Reloc Device ID
/dev/dsk/c10t500000E01013A800d0 Yes id1,ssd@n500000e01013a800
/dev/dsk/c10t500000E01013A850d0 Yes id1,ssd@n500000e01013a850
/dev/dsk/c10t500000E01013ABD0d0 Yes id1,ssd@n500000e01013abd0
/dev/dsk/c10t500000E01013B270d0 Yes id1,ssd@n500000e01013b270
/dev/dsk/c10t20000004CFAA17C8d0 Yes id1,ssd@n20000004cfaa17c8
/dev/dsk/c10t500000E01013A380d0 Yes id1,ssd@n500000e01013a380
/dev/dsk/c10t500000E01013A230d0 Yes id1,ssd@n500000e01013a230
/dev/dsk/c10t500000E01012D7A0d0 Yes id1,ssd@n500000e01012d7a0
/dev/dsk/c10t500000E010128CE0d0 Yes id1,ssd@n500000e010128ce0
/dev/dsk/c10t20000004CFC22131d0 Yes id1,ssd@n20000004cfc22131
/dev/dsk/c10t500000E01012D7B0d0 Yes id1,ssd@n500000e01012d7b0
/dev/dsk/c10t20000004CFAF377Fd0 Yes id1,ssd@n20000004cfaf377f

Thanks for the suggestion. Tried "metahs -e ...". "Hotspare isn't broken, can't enable".
Tried "metareplace -e ...", "d10: device ... enabled" It's currently in sync'ing mode. I guess drive 380 was pulled out and reinserted at one point without issuing the metareplace command.
Edited by: user8636975 on Nov 29, 2011 8:05 PM

Help - upgrading from Tiger to Snow Leopard AND new larger hard drive, MBP

Howdy!
My iPhone has finally demanded that I upgrade my MBP from Tiger. And as if by coincidence, my now puny 100GB internal drive is packed full with less than a gig free most of the time. (10% free is the MINIMUM free allowance, I know!!) I run old copies of Adobe CS2, Quark, Quickbooks, Microsoft Office... would love to keep them working without purchasing upgrades, but probably isn't a realistic hope. None of it is mission critical at this point.
So I've purchased the $29 Snow Leopard DVD (from a reseller - it says CPU Drop-In DVD Version 10.6 on the disk), and a new 750GB internal drive (same reseller - The drive is a 2.5" SATA 5400RPM 8MB-Buffer Hard Drive (9MM Slim) (RoHS Green Friendly)), to get with the times.
My other resources include:
- two 1TB LaCie external drives with FW and USB2 ports
- one other LaCie external drive - I think 360GB?
- Retrospect 5.0 (most of my backups are encrypted Retrospect files on those three LaCie external drives, but there's some room on them)
- a $22 USB 2.0 to SATA/IDE adapter with AC power, to access whatever laptop drive might be without an enclosure temporarily
- a copy of Carbon Copy Cloner software
- I just ordered an upgrade to my ancient (OS9) copy of DiskWarrior
- A monster UPS battery backup and line conditioner that everything plugs into for this process
It has been a long time since I've DIY'd any undertaking this complex, and I'm looking for advice on what to do first, how to go about this.
Here's my setup:
Model Name: MacBook Pro 15"
Model Identifier: MacBookPro1,1
Processor Name: Intel Core Duo
Processor Speed: 2.16 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per processor): 2 MB
Memory: 2 GB
Bus Speed: 667 MHz
Boot ROM Version: MBP11.0055.B08
SMC Version: 1.2f10
I'm guessing I should do it like this, PLEASE EDIT or make suggestions or tell me what I forgot to do before I do it!!
1. Back up everything to at least two external locations! Also, make a bootable copy of my current internal drive in its own volume, to at least one external drive that is formatted in HFS+ GUID partition style, with Carbon Copy Cloner (would Retrospect work well for this instead?).
2. Free up at least 20GB on the current internal drive (100GB). Hopefully 30GB.
3. Run Disk Utility on the current internal drive. Fix any problems. (Should I hit it with DiskWarrior instead?)
4. Format the new 750GB drive to HFS+, GUID partitions. (How long will that take? Can I do it with the USB-SATA cable adapter, sitting on my desk, or does it have to be in an enclosure? The adapter has AC power)
5. Run Disk Utility (or DiskWarrior?) on the new internal drive in its temporarily external position. Fix any problems.
6. Boot off the Snow Leopard CPU Drop-In DVD and install onto both drives. (Will this version of the DVD I have wipe all files when it installs to a disk???)
7. See how they run. Boot off the old 100GB internal drive, boot off the new to-be-internal 750GB drive. Panic if it's not going well.
8. If the current internal 100GB drive is rocking Snow Leopard and my familiar files and apps seem somewhat functional, use Carbon Copy Cloner to recreate the volume on the new larger drive. Then swap the drives physically. (Links to good step-by-step instructions on this part would be much appreciated here!!)
9. If the Snow Leopard DVD overwrote or snuffed out my familiar files and apps on the old internal drive, sigh deeply, then swap the drives physically. Use CCC (or Retrospect? or Migration Assistant?) to fetch my junk from the old internal drive's backup and plunk it on the new bigger internal drive (now installed).
10. See how it runs. Shake my fist at the sky over the planned obsolescence of technology paired with the seductive power of my iPhone. Grumpily upgrade the software that I actually create income with.
Please help! I am just faking it here based on a few message boards I've read. Will this actually work properly?
Thanks!

Howdy slowpoke43, and a warm welcome to the forums!
Please help! I am just faking it here based on a few message boards I've read. Will this actually work properly?
LOL, if your faking it you're the best!
1. Yes, absolutely... no CCC would be best in my experience/opinion.
2. Yes, the more he better... Free Space is no longer our Free Space, but OSX's.
3. Indeed, & if you have the correct version of DW, do that.
4. Yes, not long, A/C power is great.
How to format your disks...
http://www.kenstone.net/fcphomepage/partitioningtiger.html
(To Install OSX on an IntelMac the Drive it needs the GUID Partitioning scheme mentioned at the bottom.)
Thanks to Pondini, Formatting, Partitioning, Verifying, and Repairing Disks...
http://web.me.com/pondini/AppleTips/DU.html
6. Yes, boot off the 10.6 DVD, & no Snow Leopard does by default what we used to call an Archive & Install, saves & updates all your info, APPs, Music, etc., it may quarantine a few things or not but will tell you.
7. Absolutely, but Panic won't be needed with your great preparation & Bootable Backups!
8. Not quite sure I understand, but run SL for a few days before you do anything.
9. Yeah, but again with you doing everything right from the gitgo, I can't picture that happening.
10. Yes indeed, the hangup with yours is that it only holds 2GB of RAM... a pain in 10.5 & up IME.
Again let me say... GONGRATS, I've never ever seen anybody so well prepared & informed despite your diffidence!

Maximum safe fill for Raid-5 without hot spare?

What is the percentage of total capacity that can be used while still maintaining security blanket of the RAID-5 parity data?
I have two 7-drive arrays, neither include a spare, and simple logic suggests that the total data should not exceed the formatted capacity of six of the seven drives. Is it possible that six drives could manage, say, six-and-a-half drives worth of data via parity data, in the event the seventh drive fails?
Various G4 Mac OS X (10.4.8)

In addition to William's comment re utilization, the maximum space you can get from a 7-disk RAID 5 volume is 6 drives-worth.
That is, seven 500GB drives results in 6 x 500GB usable space, or 3,000 GB. It is not possible to extend the usable space into the seventh drive.
In RAID 5, all data is spread across all drives in the array, so there isn't actually a spare drive, or a single parity drive. RAID 3 uses a separate parity disk, but even in that configuration you cannot use space on the parity drive as user data because it's little more than a 1:1 map of the blocks on the data drives - any data on the parity space is interpreted as the parity data for the corresponding blocks on the other drives. If you stored real data in that space it would totally hose the corresponding data on the user-space disks.

MD3200i Shutdown with a Hot Spare in operation

I have to shutdown our MD3200 to make some network modifications tied- iSCSI and vCenter (replacing a switch)
One of the MD3200 drives failed and the hot spare is being used (RAID 5).
Is it safe to bring down the Md3200 while the hot spare is in operation ?
thanks

Hello SJNAPL,
If the drive failed a few months back then it has most likely been copied to the hotspare. You should be able to use MDSM & go to the Physical Tab & select the hotspare drive & it will list the drive that it is covering.
Once you get your replacement drive and insert it into your MD3200i the MD will sense the drive & should start the copy back to the replacement drive. Now the time that it will take is hard to say as it depends on the size of the drive and how much activity is on the virtual disk.
Once the replacement disk has the data from the hotspare then the hotspare should go back to being a hotspare drive again & you can view this also in the summary window of MDSM& the Physical Tab as well.
Please let us know if you have any other questions.

Hot spare

Should I leave a drive out of the raid setup to create a Hot Spare? Hot Spare?are automatically added if a drive goes down right?

> Should I leave a drive out of the raid setup to create a Hot Spare?
Should you? That's up to you to decide based on a number of factors including how long you're prepared to run with a failed drive in thebox, how much storage you need (if you can afford to lose one (or two) disks' worth of storage).
> Hot Spare?are automatically added if a drive goes down right?
Correct. If a drive fails and you have a hot spare then the RAID automatically initiates a rebuid on the spare. This can take some time, especially for large arrays, during which time you risk losing your data should another drive fail.
If you don't have a hot spare then you need to manually replace the drive. This adds an extra amount of time to the window where you risk losing data, ranging from minutes (you notice straight away and have a spare disk sitting on a shelf) to days (you're away on vacation and don't notice).
FWIW, in all the XServe RAIDs I've run for years I've had one single disk failure.

Hot spare and identifying volumes to drives.

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