Write amplification of RAIDZ/RAIDZ2 on SSDs?

5mall5nail5

Dabbler
Joined
Apr 29, 2020
Messages
14
Hey all - I am putting together an all-flash FreeNAS array using a pool of (10) Samsung PM863 960GB SSDs and (12) Intel S3710 400GB SSDs. I've always used mirrors for SSD pools/RAID, but thinking about RAIDZ (spanned or not) variations... but am concerned about write amplification when using SSDs which ultimately have a limit of DWPD. Anyone have an opinion or information?

The Intel S3710 are high-endurance write disks, so I am thinking of trying RAIDZ2/3 across those (proably 2 since they're only 400GB so rebuild times will zip). But the PM863s are "general purpose" - maybe stick to mirrors? I am just looking for peoples experience - thanks!
 

AlexGG

Contributor
Joined
Dec 13, 2018
Messages
170
I have an opinion (based on data layout on disks, not practical measurement). There will be no difference in write amplification as it applies to SSDs, because write patterns are not really that different between mirror and RAIDZ. However, as redundancy overhead is lower with a RAIDZ compared to a mirror, your overall write amount will be lower, and thus SSDs should last longer in a RAIDZ than in a mirror.
 
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