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RAID 5 with 4 1TB drives and RAID card

kittiyut

kittiyut

macrumors 6502
Original poster
I did a search on this but couldn't find anything, so here's my question:

I'm getting the new Mac Pro 8 core 3.2 with the RAID card (getting the
4 Seagate 1TB 7200.11 drives separately - why pay APPLE that much?)
I want to do RAID 5 for both redundancy and performance and not lose
too much capacity (like you do in RAID 0+1) what would you guys do;

- use all 4 drives in RAID 5
- use 3 in RAID 5 and 1 for the OS (does this make sense?)
for this option, there's no redundancy for the lone drive.

what do you experts out there think? 😕😕

KK
 
I'm a great fan of RAID 5 + hot spare (which is how I usually configure servers), but under the circumstances, that's not an option here - I'd go for 4 drives in the array.
 
Place them into a single array, then create a seperate partition for OS so that you have the logical seperation and still maintain the performance and fault tolerance of RAID 5.

Do NOT forget to backup important data, as RAID is only tolerant of drive faults, and does not cover file corruption or unintended deletes/user errors.
 
whats the volume size

if he puts all 4 1tb drives into the raid 5 array, what is the volume size? how many drives can fail and still be okay?
 
I would put 3 drives in the RAID 5 and all data there should be safe against drive failure. I would then use the 1 drive that isn't in the RAID as your system drive and have Time Machine back it up to the RAID array. In a RAID 5, one drive is always used for redundancy so you would lose the capacity of that drive... You might able to stick a drive in the 2nd optical drive bay...
 
Rick Here said:
The volume will be roughly 3/4 of the entire 4 drives or 3TB since one drive will used for the parity to protect the array.
Click to expand...

Wrong. RAID 5 distributes the parity across the array, not just in one
particular drive - that's RAID 4. However, you are correct that the amount
of space will be 3TB since all 4 drives are the same capacity (1TB) 😉
 
kittiyut said:
Wrong. RAID 5 distributes the parity across the array, not just in one
particular drive - that's RAID 4. However, you are correct that the amount
of space will be 3TB since all 4 drives are the same capacity (1TB) 😉
Click to expand...

Yes. For example, my Athlon PC is running a RAID 5 array with 7 x 250 GB HDD, but I only have the usable capacity of 6 x 250 GB. It's always the number of drives less 1. ANY drive can fail and the array would be fine, but no longer redundant. (RAID 6 capacity is number of drives less 2)
 
kittiyut said:
Wrong. RAID 5 distributes the parity across the array, not just in one
particular drive - that's RAID 4. However, you are correct that the amount
of space will be 3TB since all 4 drives are the same capacity (1TB) 😉
Click to expand...

Excuse Me ! I meant one drive capacity. Yes the parity is distributed across the entire set of drives.
 
I have my 4 750's in a RAID5. Within that array I have two volumes. One 300GB volume for the OS and Applications and the rest of the 1.5TB as a storage volume which also has my home directories. I accidentally wiped out my OS volume and it was really nice having my home directory somewhere else.
 
I Was Told By An Apple Expert At MacWorld To Only Raid 5 Three Drives, Not Boot Drive

9Charms said:
I would put 3 drives in the RAID 5 and all data there should be safe against drive failure. I would then use the 1 drive that isn't in the RAID as your system drive and have Time Machine back it up to the RAID array. In a RAID 5, one drive is always used for redundancy so you would lose the capacity of that drive... You might able to stick a drive in the 2nd optical drive bay...
Click to expand...
I got my four 1TB Seagate drives on sale at Fry's the weekend before MacWorld for $270 each. I'm getting the same 3.2GHz Mac Pro you are with the Raid card. An expert at the Mac Pro part of the Apple booth told me NOT to Raid 5 all four. He said to Raid 5 three beyond the boot drive. I plan to follow his advice.

Yes one PATA drive easily fits under the optical so a total of 5 drives are possible inside.
 
65StangBoy said:
I have my 4 750's in a RAID5. Within that array I have two volumes. One 300GB volume for the OS and Applications and the rest of the 1.5TB as a storage volume which also has my home directories. I accidentally wiped out my OS volume and it was really nice having my home directory somewhere else.
Click to expand...

Wow, how did you "accidentally" wipe it all out? Mind sharing so we don't make the same mistake??🙄
 
kittiyut said:
Wow, how did you "accidentally" wipe it all out? Mind sharing so we don't make the same mistake??🙄
Click to expand...

Yeah, it was stupid but atleast I learned something. I was trying to get GRUB to boot my Windows XP partition and was having problems so I had to wipe out the MBR. I read somewhere that it wouldn't be a problem to do that since OSX didn't use that part of the drive. WRONG!!! Wiped it and all of a sudden my OS volume was trashed. No biggie since my home directory was on another volume. Just had to reinstall the OS and my applications. Lesson learned.
 
MacRoom said:
An expert at the Mac Pro part of the Apple booth told me NOT to Raid 5 all four. He said to Raid 5 three beyond the boot drive. I plan to follow his advice.
Click to expand...

Really? What reasons does he give? Why 3?

I'd be tempted to RAID as many drives as possible to reduce the wasted overhead. However, I definitely would not RAID my boot drive or scratch drive as it would slow the computer down and become a bottleneck.
 
I can't think of any reason why they would suggest only running a three drive RAID5. The more spindles you have in your RAID5, the better the performance.
 
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