Time Machine backup FROM multiple drives?

Question

I'm in the process of choosing a new MacPro, someone on these forums recommended Digilloyd's Mac Performance Guide as a good place to get help setting up a new mac for speed. The simplified version of what he advocates is replacing the stock internal drive with an SSD drive, on which you put the OS, apps & home folder. He then recommends creating a 0-raid stripe from 3 other drives to separate & hold your data, then using the forth internal bay drive (or another 0-raid stripe of the leftover, slower portions of various partitions of the drives) for Time Machine.
My question is, can Time Machine backup both drives (boot & data raid-0) or would I have to choose one of them?
+The more I read, the more confused I get+.

Answer 1

OK, I've scanned through the various articles. My thoughts are still essentially the same, and that is just how effective the entire system is when using multiple partitions from several drives to combine into multiple RAIDs. In reality this is not speed effective if the RAIDs need to be accessed concurrently. A read/write head can only be in one place at a time meaning that when one partition on the drive is being accessed, the OS cannot concurrently access another partition on the same drive.
Essentially this is how I understand the configuration at a simplistic level. Let's suppose we have two hard drives that we'll call Drive A and Drive B. Each drive is partitioned into two equally sized volumes that we'll refer to as follows:
....................... *Drive A* ......................... *Drive B* ......
Volume................. 1 ..................................... 3 ............
Volume................. 2 ..................................... 4 ............
Now, we will make two RAID arrays. RAID A uses Volume 1 and Volume 3, and RAID B uses Volume 2 and Volume 4.
Suppose you want to copy data from RAID A to RAID B. In order to do this the OS must first copy data from RAID A before it can write the data to RAID B. However, if RAID A was created using two separate drives (say, Drive A and Drive B,) and RAID B was created using two separate drives (say, Drive C and Drive D,) then the OS can copy from RAID A while concurrently writing to RAID B. This is physically possible because two read/write heads are involved instead of one. Theoretically the second construct is going to be much faster than the first construct.
My second observation is with regard to the reliance on external storage. A 2nd or 3rd generation Mac Pro's SATA bus is capable of a data interface rate of 3.0 Gb/sec. Firewire 800 is capable of 800 Mb/sec. The MP's internal SATA bus can support data transfer rates nearly four times that of Firewire. A modern hard drive is capable of saturating the Firewire bus, but not the internal SATA bus. The higher interface rate of the SATA bus means it's much better suited for truly fast RAID arrays. This is not the case for the Firewire bus.
External Firewire arrays are better suited for storage that does not require frequent or fast access.
Now with all this said it makes more sense to fully understand what your overall storage needs are then consider suitable designs. One need not rely on complicated RAID arrays if they aren't required. The focus should be on data access, data storage, and backup needs.
Although it's nice being able to brag at the cocktail party about having a fast SSD for your boot drive, let's consider how often you even need to boot the computer. I put my computers to sleep when they aren't in use. I never boot the computer unless a software update requires it or the computer has crashed completely. I haven't had the latter occur very often - mainly when I'm experimenting. Literally days, weeks, or months may go by before I reboot the computer. So a fast SSD boot drive would be for me a hugh waste of money.
My 1st generation Mac Pro is set up for my needs. It has four 500 GB fast Hitachi enterprise level hard drives. I use enterprise level drives that cost more because the computer is always on, so I want drives that will be reliably working. I used to have four Maxtor 300 GB drives that lasted for four years before I replace them with the Hitachis. My setup has one drive partitioned into a startup volume and a Boot Camp volume. One drive is my 'scratch' drive used for different OS system versions and/or seed testing. Two drives are configured as a mirrored RAID and used as the primary backup for the boot volume. The boot volume is 450 GBs and the Windows volume is 50 GBs. There's no backup for the Windows volume at the present time. Backups are usually done in the late afternoon using a backup utility. Presently that utility is Synk Standard, but I've also used Synchronize! Pro X and Carbon Copy Cloner. Backups are done on a fixed schedule in the background so they are virtually transparent to me. I use a mirrored RAID for backup to provide redundancy. If one backup drive fails hopefully the other will still be usable to protect the backup. I also have one external Firewire drive that contains a clone of the startup volume. The clone is updated monthly by incremental backup. It's for security in the worst case scenario that both drives in the mirrored RAID were to fail simultaneously.
Now, my need for frequent and fast access to data such as might be needed for streaming music or video is non-existent, so my configuration is one that is well-suited to my needs. You'll note that it's both simple and practical while providing data backup that's doubly secure.