SSD raid array, should I pick 0 or 5?

Question

Currently I have a raid0 SAS array in my system (I know, you must think I really hate my data to have this) and really like the performance over a single disk. A couple months back I built a new system for myself at work which is using SSDs and can't believe the performance of them. I was planning on upgrading to them in the coming weeks/months on my home computer now.

I know the performance of a single SSD is well beyond what my current setup is

My work system's SSD array

Storage disk

However I’d like to go with multiple smaller disks instead of 1 larger one like I did with the SAS drives. Would I be ok with raid0 here again or should I avoid that and go right for raid5? I’ve setup the backup process in Windows7 to back up my data to a 2TB drive I have and as soon as my new server is up and running I’ll be backing up to there, which will have a raid5 array like my current one. I’m just wondering if raid0 in this case is really that bad as long as my data is backed up.

Another question I had was if I’m able to grow the array once it’s built. So if I had say 2 50GB drives in there totaling 100GB and then bought another 50GB could I grow the array size to 150GB or would I have to create a new array and then reinstall?

Solution

Advantages of RAID 5 in your setup:

• You can add disks to increase the storage without having to reinstall the operating system or recover data.
• RAID 5 is fault tolerant. You are very very unlikely to have more than one disk fail at the same time (although I did just see this for the first time at a client - gulp), so there is much less chance of having to rebuild your system from scratch
• If a disk fails with RAID 5, you can simply replace the disk and rebuild/resync the array. If a single disk fails with RAID 0, bye bye data on both disks.
• If you were to stick with RAID 0 and a daily backup, restoring from the backup would result in data loss between when the last backup was taken and when the disks failed.

Disadvantages of RAID 5 in your setup:

• There is a performance hit when writing, over a RAID 0 striped array.
• You need at least 3 disks.
• You effectively lose the capacity of one of the disks (although the parity data is spread across all disks).

RAID 5 is common for business servers that hold mission critical data and require maximum uptime. Otherwise, if speed is the dominating requirement in your setup and a loss of maybe a few hours work is acceptable, then go for RAID 0.

Comments

[Admin]

I think to grow it you'd need to use LVM or similar, but I've not tried what you're describing :)

[Admin]

There are advantages to having a larger SSD compared to a smaller one though. The SSD controller essentially puts each NAND chip in a RAID 0, so larger SSDs are faster, like RAID (though performance benefits are less significant for PCIe SSDs, they also teeter out past 1 GB/s on normal RAID). There are also the wear leveling advantages, and of course, they take up fewer ports. You could always set up RAID later. EDIT: Huh, just realized how old this is. nvm

[huy]

I think performance on RAID5 on SSD is going to be negligible.

[John Rose]

Intel's onboard RAID is really good for SSDs in RAID-0, actually. I have one machine with with an Intel ICHR7 and another with a Intel ICHR10, each running two SSDs in RAID-0. Unlike RAID-5, RAID-1 and RAID-0 require very little computational power. They just need bandwidth. According to the OCZ forums it seems the ICH chips can handle up to at least three Vertex SSDs in RAID-0 before they start hitting the limits of the ICH.