NFS writes on ZFS blows chunks performance wise. The only way to increase the write speed is by using an slog, the problem is that a "proper" slog device (one that doesn't lose transactions) does not exist for a reasonable price. The least expensive SSD that will work is the Intel X25-E, and even then you have to disable the write cache, which kills performance. And if you lose transactions in the ZIL, you may as well not have one.
Switching to a pool configuration with mirrors might help some. You will still get hit with sync write penalties on NFS though. Before messing with that, try disabling the ZIL entirely and see if that's where your problems are. Note that running without a ZIL can cause you to lose about 30secs of uncommitted data and if the server crashes without the clients rebooting, you can get corrupted data (from the client's perspective). However, it solved the performance issue for me. If that works, you can then decide how important the ZIL is to you. Personally, I like things to be correct, but that doesn't help me if performance is in the toilet. In my case, the server is on a UPS, the clients aren't. And most of the clients use netboot anyway, so they will crash and have to be rebooted if the server goes down. So for me, the drawback is small while the performance gain is huge. That's not the case for everyone, and it's up to the admin to decide what they can live with. Thankfully, the next release of OpenSolaris will have the ability to set ZIL on/off per filesystem. Note that the ZIL only effects sync write speed, so if your workload isn't sync heavy, it might not matter in your case. However, with NFS in the mix, it probably is. The ZFS on-disk data state is not effected by ZIL on/off, so your pool's data IS safe. You might lose some data that a client THINKS is safely written, but the ZFS pool will come back properly on reboot. So the client will be wrong about what is and is not written, thus the possible "corruption" from the client perspective. I run ZFS on 2 6-disk raidz2 arrays in the same pool and performance is very good locally. With ZIL enabled, NFS performance was so bad it was near unusable. With it disabled, I can saturate the single gigabit link and performance in the Linux VM (xVM) running on that server improved significantly, to near local speed, when using the NFS mounts to the main pool. My 5400RPM drives were not up to ZIL's needs, though they are plenty fast in general, and a working slog was out of budget for a home server. -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
