In what use case is a RAID 1E preferable to a RAID 5 array on a 3 disk array?

Question

This question has got a bunch of us talking in chat, and it had me wondering:

Most of RAID 5's ugly characteristics like UREs and long rebuilds present themselves in much larger arrays. With a RAID 5, you'll have 66% disk space available and can sustain 1 disk failure. With a RAID 1E, you'll have 50% disk space available and can also sustain 1 disk failure.

Given a three disk array, in what case would it be preferable to use a RAID 1E over a RAID 5?

Solution

If you don't have a write cache, the parity calculation for writes, especially random writes, will be higher on raid-5 than some non-parity based raid like raid-1E.

Comments

[MDMarra]

So, if you have a high write workload and, for some reason, are stuck with a 3-disk array to handle this workload and not enough write cache to overcome the write penalty, then RAID 1E would be a better solution?

[Basil]

Yeah, if you have enough random writes that your cache can't completely buffer them (or if you have writethrough enabled), something without parity calculations would be a way of getting around it. Raid 1E and raid 10 don't use parity.