Hello,
We have performed several tests to measure the performance using SSD drives for the ZIL. Tests are performed using a X4540 "Thor" with a zpool consisting of 3 14-disk RaidZ2 vdevs. This fileserver is connected to a Centos 5.4 machine which mounts a filesystem on the zpool via NFS, over a dedicated, direct, 1Gb ethernet link. The issue we're trying to resolve by using SSD's, is the much-discussed slow NFS performance when using synchronous IO. Unfortunately, asynchronous IO is not possible, since the Solaris NFS server is synchronous by default, and the linux clients are unable to request asynchronous NFS traffic. The SSD devices we've used are OCZ Vertex Turbo 30Gb disks. Data was gathered using iozone from the centos machine: (iozone -c -e -i 0 -i 1 -i 2 -o -a). The raw data as well as the graphs that I created are available on request, should people be interested. Since we are interested in using the Thor as an NFS file server for homedirectories, we are mostly concerned about random write performance. We have made the following observations: - Using SSD devices as ZIL logs yields a factor 2 improvement in throughput when using a recordsize <= 128k, in comparison to using the internal ZIL devices of the pool (ie. not setting up slog devices). - With recordsizes of 1MB and up, having the ZIL reside on the raw disks of pool (no separate slog devices) outperforms using SSD's as a slog device. - Disabling the ZIL altogether yields significantly better performance (at least a factor 10). We had hoped that using SSD's would yield better performance. It is possible we will see an improvement with Intel X25-E series SSD's, but those haven't arrived yet so we can't test that. An alternative test we performed was extracting a 138Mb tarfile consisting of ~2000 small files. With the ZIL disabled, extracting the file took 4 seconds. With the ZIL enabled, but with no specific slog devices in the pool (thus using the disks in the pool), extraction took 72seconds. Using the SSD's as log devices, the time required was reduced to 34 seconds. This corresponds to the ~factor 2 improvement we noticed using our iozone benchmark. For this specific workload, we noticed no difference in using 1 or 2 (striped) slog SSD's. At the bottom line, lets end up with a few specific questions: 1. Is this performance using SSD's as expected? Can we expect better performance using Intel X25-E SSD's? 2. Disabling the ZIL looks like a serious option, after these performance benchmarks. I would expect to see Disabling the ZIL as an "officially supported option", given that we all have used UFS for years, which is no better in terms of reliability. Is there an "Official Sun Response" to this? with kind regards, Auke Folkerts University of Amsterdam
pgpdRrzeL41WP.pgp
Description: PGP signature
_______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
