(Software) RAID-1 (Mirror) under Mac OS X

[ionas]

Anyone got some expirience if and how good Software RAID works under Mac OS X on a G5?

IDE Harddrives often die if you run your computer 24/7/mostdaysoftheyear. It happend to me often and I want to keep my data save.

Are there Hardware RAID Controllers that dont cost too much (it is just for two or 4 drives creating 1 or 2 virtual devices) around? Do they work perfectly with the G5 and MAC OS X?

 

[Tiauguinho]

Im gonna do a RAID 1 on my Xserve as soon as it arrives (this week or next week). I can post a step by step procedure for you to do it as well.

 

[ionas]

Hm

But that will Ship MAC OS X Server
Will you do it software or hardware based?

 

[tomf87]

If you're looking to keep the performance hit to a minimum, I'd strongly advise going with a hardware solution. Software solutions, while they work, add an addition hit on performance, as the OS has to do the mirroring, while the hardware solution offloads that task from the main CPU(s).

 

[ionas]

hmm

If you're looking to keep the performance hit to a minimum, I'd strongly advise going with a hardware solution. Software solutions, while they work, add an addition hit on performance, as the OS has to do the mirroring, while the hardware solution offloads that task from the main CPU(s).

Well I do not want an ugly slow monster.
I want to use photoshop files but they aren't bigger than 25mb most times, listen to mp3s, connect to my webserver that might ship 500kb/sec and max impression sizes of maybe 500kb, sometimes move large files and list lots of small files (like load a list of 10000 fonts or 10000 music files or 10000 textures).

i dont want to have the same crappy feeling i get on usual windows machines where you move files and everything hangs (even if you got 512mb ram).

if that is the case i will spend 200 eur on hardware raid. but it wont get below - i asked a local reseller for the lowest price for any ide hardware raid controller; he didnt even know if it was g5 compatible.

can you recommend any hardware raid controller that is made for the g5? (and maybe is pci-x 133mhz ;-)

can i use 2 disks that where created with software raid on mac os x on a hardware raid controller (is there a standard so that it will run both and i can update if i see that it is "crap slow")?

 

[Bigheadache]

If you're looking to keep the performance hit to a minimum, I'd strongly advise going with a hardware solution. Software solutions, while they work, add an addition hit on performance, as the OS has to do the mirroring, while the hardware solution offloads that task from the main CPU(s).

Thats mainly true for RAID 5 or where parity has to be calculated. In RAID 1 I doubt it would be that big a hit on performance.

 

[ionas]

just to recap

raid 1 = mirroring (2x80gb = 1x80gb save data

 

[Bigheadache]

I don't think you need a hardware RAID controller if you just use RAID 1. There is no parity calculation required. But if you insist, check out the Adaptec and ATTO range.

 

[ionas]

if i ever want to switch from raid 1 to raid 5

(raid 0 = stripe)
(raid 1 = mirror)
(raid 5 or 1+0 = mirror and stripe)

I just need 1 or 1+0 (which would work with 3 harddisks); could i switch from software raid on mac os x to hardware raid (just build in the raid controller, install the drivers and there i go)?

the g5 doesnt even has place for 3 harddrives + optical drive right?
maybe the rev. b has.

well i think i ll be happy with raid 1 - so thanks for your tip!

 

[tomf87]

(raid 0 = stripe)
(raid 1 = mirror)
(raid 5 or 1+0 = mirror and stripe)

RAID 5 and RAID 1+0 are not the same. RAID 0 is striping without parity. RAID 5 is striping with parity. RAID 1+0 is a combination of RAID 1 and 0. You'll need at least 4 disks for RAID 1+0. For example, let's say you have the following four hard disks, all at 80GB:

Hard Disk 0
Hard Disk 1
Hard Disk 2
Hard Disk 3

Hard Disk 0 and 1 will be mirrored to become Volume 1 (80GB). Hard Disks 2 and 3 are mirrored to become Volume 2 (80GB). Then Volume 1 and Volume 2 are together in a RAID 0 to become Volume A (160GB). In this scenario, you can lose one hard disk from Volume 1 and one hard disk from Volume 2 and still be functional. If you lose two hard disks from Volume 1 or lose two hard disks from Volume 2, you've lost your data.

EDIT: Also RAID 1 and 1+0 are different. You just need two drives for RAID 1 which will work in the current G5's.

 

[tomf87]

Thats mainly true for RAID 5 or where parity has to be calculated. In RAID 1 I doubt it would be that big a hit on performance.

RAID 5 does require more overhead than RAID 1, however, any time the OS has to handle two reads or writes rather than one, there's a performance hit. I doubt it would be that big of a hit too, but ATA RAID cards are fairly inexpensive so it may be worth the cost.

 

[Bigheadache]

RAID 5 does require more overhead than RAID 1, however, any time the OS has to handle two reads or writes rather than one, there's a performance hit. I doubt it would be that big of a hit too, but ATA RAID cards are fairly inexpensive so it may be worth the cost.

Generally the biggest cost of RAID is calculating the parity stripe, not actually the cost of read/writes. My experience tends to be on the PC side, where there isn't really a material performance hit to RAID 1 using the Intel ICH5R Southbridge. I think this is maybe because RAID 0,1, 0+1, is supported "in hardware", so the system thinks its doing one read/write, and the southbridge is handling the RAID aspect. I am not sure if the Apple G5 system controller does this as well. If it doesn't, then yes you might want to choose a RAID controller. At least if you get a decent one you can also think about RAID 3 or 5.

 

[tomf87]

Generally the biggest cost of RAID is calculating the parity stripe, not actually the cost of read/writes. My experience tends to be on the PC side, where there isn't really a material performance hit to RAID 1 using the Intel ICH5R Southbridge. I think this is maybe because RAID 0,1, 0+1, is supported "in hardware", so the system thinks its doing one read/write, and the southbridge is handling the RAID aspect. I am not sure if the Apple G5 system controller does this as well. If it doesn't, then yes you might want to choose a RAID controller. At least if you get a decent one you can also think about RAID 3 or 5.

You're exactly right. My last software RAID was in the NT 4.0 days in 1997. Back then, the motherboards didn't have anything fancy on them. Maybe that's why I saw a performance hit whenever any type of software RAID was used.