SLOG to improve NFS

[trumee]

Hello,

I use NFS between the linux servers and FreeNAS server. The NFS improves from 30MBps to 100 MBps if i disable 'Sync writes' on the FreeNAS server. It seems i need an SLOG to improve the sync writes.

I was planning to add an Intel 750 PCIEX SSD 400 GB to the pool.
1) Do i need a mirrored device or is a single card is sufficient?
2) Can i add an SLOG after the pool has been created?
3) If 400GB big for an SLOG, can i partition the drive and use the remaining space for something else?

Thanks

PS: I use 2x4TB setup in a mirror on X10SL7-F with 32GB Ram and E3-1231 v3 CPU.

 

[dlavigne]

1) Do i need a mirrored device?

No. From http://doc.freenas.org/9.10/zfsprimer.html#zfs-primer:

The log device does not need to be mirrored on a pool running ZFSv28 or feature flags as the system will revert to using the ZIL if the log device fails and only the data in the device which had not been written to the pool will be lost (typically the last few seconds of writes).

2) Can i add an SLOG after the pool has been created?

Yes. See http://doc.freenas.org/9.10/freenas_storage.html#extending-a-zfs-volume.

3) If 400GB big for an SLOG, can i partition the drive and use the remaining space for something else?

No. From http://doc.freenas.org/9.10/zfsprimer.html#zfs-primer:

Note that a dedicated log device can not be shared between ZFS pools and that the same device cannot hold both a log and a cache device.

 

[trumee]

I am upgrading my computers to 10 gigabit. I guess an SLOG will not be able to match the 'disabled sync' speeds. How much NFS write speed can i expect from Intel 750 SSD?