Can a RAID do this?

[-hh]

Just read a different thread that was discussing setting up of multiple partitions on three drives set up as a RAID 0. Basic idea was to have a scratch disk for Photoshop.

...which got me thinking in a perpendicular direction.

Without going into esoteric RAID levels (eg, 10, 50, etc), is the following notionally possible? Assume a new Mac Pro:

Bay 1: Boot drive - present, but being ignored for this conversation.
Bay 2: big old HD "A"
Bay 3: big old HD "B"
Bay 4: (vacant)

Step 1: Partition A into a 100GB + 0.9TB split (A1, A2)
Step 2: Partition B into a 100GB + 0.9TB split (B1, B2)
Step 3: RAID partitions A1 + B1 ... as a RAID 0
Step 4: RAID partitions A2 + B2 ... as a RAID 1

Pass/Fail?

The basic question is: can this really be done with this few spindles?

The follow-up question is: is this a good-bad-horrible-etc idea?

The basic intent behind this is to try to "have my cake and eat it too" by having a small fast scratch space (RAID 0) and a large RAID 1 protected storage space, but the question is to what degree can the total number of physical drives be minimized? Thus, is 2 possible? And even if it is, what are the recommended alternatives? I'm inclined to go with 3 bays for a RAID 5, for example, but I'm unclear as to which would be a better/worse performer and in what area the trade-offs exist.

-hh

 

[robinp]

Just read a different thread that was discussing setting up of multiple partitions on three drives set up as a RAID 0. Basic idea was to have a scratch disk for Photoshop.

...which got me thinking in a perpendicular direction.

Without going into esoteric RAID levels (eg, 10, 50, etc), is the following notionally possible? Assume a new Mac Pro:

Bay 1: Boot drive - present, but being ignored for this conversation.
Bay 2: big old HD "A"
Bay 3: big old HD "B"
Bay 4: (vacant)

Step 1: Partition A into a 100GB + 0.9TB split (A1, A2)
Step 2: Partition B into a 100GB + 0.9TB split (B1, B2)
Step 3: RAID partitions A1 + B1 ... as a RAID 0
Step 4: RAID partitions A2 + B2 ... as a RAID 1

Pass/Fail?

The basic question is: can this really be done with this few spindles?

The follow-up question is: is this a good-bad-horrible-etc idea?

The basic intent behind this is to try to "have my cake and eat it too" by having a small fast scratch space (RAID 0) and a large RAID 1 protected storage space, but the question is to what degree can the total number of physical drives be minimized? Thus, is 2 possible? And even if it is, what are the recommended alternatives? I'm inclined to go with 3 bays for a RAID 5, for example, but I'm unclear as to which would be a better/worse performer and in what area the trade-offs exist.

-hh

sounds very interesting... surely the thing to do is try it?

 

[bozz2006]

yeah, let us know how it works!

 

[mackmack]

If you have stuff going on the RAID 1 set it kind of negates the performance advantage of the RAID 0 array because the drive will be bogged down with the RAID 1 activity.

I think it would be better to just have the two drives as RAID 1.

 

[POLOgt]

Your best option is to put a scratch disk in Bay 4,
That will give you the best performance for our scratch disk, and just keep your two "Bid old HD" in RAID1

 

[-hh]

If you have stuff going on the RAID 1 set it kind of negates the performance advantage of the RAID 0 array because the drive will be bogged down with the RAID 1 activity.

Agreed, although I think that this would be adequately addressed by workflow: the RAID 0 is mostly for Photoshop scratch space, whereas the RAID 1 is for "permanent" storage after the image(s) have been worked on.

I think it would be better to just have the two drives as RAID 1.

Agreed; just trying to see if there's a fairly easy way to cheat.


-hh

 

[-hh]

sounds very interesting... surely the thing to do is try it?

Fair enough, although I'm hoping that someone else will get to it months before I will: I'm not planning on placing my Mac Pro order for a couple of months, as I want to make sure to also get Snow Leopard.


-hh

 

[fatespawn]

-hh,

My .02?

Buy a 10,000RPM 74 GB WD Raptor drive from ebay for a "buy it now" price of $60 for your scratch disk.

Then don't mirror your other 2 "large drives." Clone them nightly. Unless "real time" redundancy is absolutely crucial, you'll get a longer life out of both drives if you just clone them nightly and swap which one you work off every few months or so.

-fate

 

[NoNameBrand]

I use an 8-9GB partition on four of the five drives in my G5 (eSATA) as a stripped array for scratch (only use). three of the component disks get very little use while I'm Photoshopping, so I probably should have limited the array to those three and not included the boot/apps drive, but the speed of the array is very fast compared to a single disk in my G5.