SLOG Questions

[Derek Zeanah]

I read somewhere that the failure of an SLOG device was a really bad thing, which meant it made sense to mirror your SLOG SSDs.

I've read more recently that current (> v 15) versions of ZFS don't have this issue, and a failure of an SLOG device only affects performance (assuming the failure doesn't happen immediate before a system outage where the data on the SLOG is important for recovery.)

So, in my NAS4Free build does this mean I should not create a vdev mirror of SSD drives, and instead should just use one?

It looks like multiple L2ARC drives are striped; can we do the same thing with SLOGs to increase performance, or is only one supported?

Thanks.

[chrisf4lc0n]

It depends on how you use your N4F, if many random sectors are being accessed at the same time by many users, then it may make sense to strip the logs, in a home environment where data are mostly streamed linearly it would not result in an increased performance.

[Derek Zeanah]

It depends on how you use your N4F, if many random sectors are being accessed at the same time by many users, then it may make sense to strip the logs, in a home environment where data are mostly streamed linearly it would not result in an increased performance.

Thanks. I'm running iometer against my server with no SLOG in place and things are flying as long as I keep things async. I'll test again using sync, then again using an SSD SLOG and report back.

(In my case the server will be used for VM storage, and 40% of those VMs will be database servers, so IOPS is what I'm focusing on.)