Can I use 2x 1TB 64MB Cache and 1x 1TB 32MB Cache in a RAID 5 setup?

Question

I've been told the drives have to be identical for RAID 1, but when searching for additional drives in local stores to match:

WD 1TB Caviar Black 7200rpm SATAII w/ 32MB Cache

They say they don't carry those anymore but they do have the same drive w/ 64MB Cache instead. They also told me that RAID 5 was not as finicky as RAID 1 and that it would probably be fine to use the combination of 3 drives with 1 having 32MB cache and 2 having 64MB cache.

Does anyone know this to be true? Does cache have to match when doing RAID 5?

Thanks,
Matt

Answer 1

You don't mention which disk controller you've got, if you want hardware RAID then there's a remote chance that mixing disks may not be supported (check with controller documentation) but almost certainly they'll be fine. If it's software RAOID it'll definitely be just fine.

Answer 2

It is always better to use hard drives of the exactly same model (with the identical part numbers). Even if you got lucky and the different drives are supported, using the hard drives of different series is going to become a problem, when you need your array to be fast. You can use even different sized disks, but the array will work slowly and unstable. Don't do that, please.

See Tom's Hardware for more detailed information.

Answer 3

You want to disable the disk cache regardless, so the size doesn't matter.

If you leave the disk cache on, during a power issue you could lose data. The raid array says it is committed, but in fact the data is still in the disk cache which is lost with a power outage.

There isn't really isn't a penalty for using different drives, its just that on average you're not going to perform faster than the slowest disk. I think the Tom's Hardware article shows that.

Now, if one disk has slow access and the other slow transfers, you could end up with the worst of both worlds. But the thing that actually matters is is the array still fast enough for what you need to do, versus the cost of replacing the non-matching drives.

Answer 4

I couldn't figure out how to comment below your question but you can still get 32mb cache drives at bestbuy for 89 bucks. I just purchased one and they price matched the web price at the register.

Best Buy Link