On Mon, May 9, 2011 at 8:33 AM, Darren Honeyball <ml...@spod.net> wrote: > I'm just mulling over the best configuration for this system - our work load > is mostly writing millions of small files (around 50k) with occasional reads > & we need to keep as much space as possible.
If space is a priority, then raidz or raidz2 are probably the best bets. If you're going to have a lot of random iops, then mirrors are best. You have some control over the performance : space ratio with raidz by adjusting the width of the radiz vdevs. For instance, mirrors will provide 34TB of space and best random iops. 24 x 3-disk raidz vdevs will have 48TB of space but still have pretty strong random iops performance. 13 x 5-disk raidz vdevs will give 52TB of space at the lost of lower random iops. Testing will help you find the best configuration for your environment. > HP's recommendations for configuring the MDS 600 with ZFS is to let the P212 > do the raid functions (raid 1+0 is recommended here) by configuring each half > of the MDS 600 as a single logical drive (35 drives) & then use a basic zfs > pool on top to provide the zfs functionality - to me this would seem to loose > a lot of the error checking functions of zfs? If you configured the two logical drives as a mirror in ZFS, then you'd still have full protection. Your overhead would be really high though - 3/4 of your original capacity would be used for data protection if I understand the recommendation correctly. (You'd use 1/2 of the original capacity for RAID1 in the MDS, then 1/2 of the remaining for the ZFS mirror.) You could use non-redundant pool in ZFS to reduce the overhead, but you sacrifice the self-healing properties of ZFS when you do that. > Another option is to use raidz and let zfs handle the smart stuff - as the > P212 doesn't support a true dumb JBOD function I'd need to create each drive > as a single raid 0 logical drive - are there any drawback to doing this? Or > would it be better to create slightly larger logical drives using say 2 > physical drives per logical drive? Single-device logical drives are required when you can't configure a card or device as JBOD, and I believe its usually the recommended solution. Once you have the LUNs created, you can use ZFS to create mirrors or raidz vdevs. > I'm planning on having 2 hot spares - one in each side of the MDS 600, is it > also worth using a dedicated ZIL spindle or 2? It would depend on your workload. (How's that for helpful?) If you're experiencing a lot of synchronous writes, then a ZIL will help. If you aren't seeing a lot of sync writes, then a ZIL won't help. The ZIL doesn't have to be very large, since it's flushed on a regular basis. From the Best Practices guide: "For a target throughput of X MB/sec and given that ZFS pushes transaction groups every 5 seconds (and have 2 outstanding), we also expect the ZIL to not grow beyond X MB/sec * 10 sec. So to service 100MB/sec of synchronous writes, 1 GB of log device should be sufficient." If the MDS has a non-volatile cache, there should be little or no need to use a ZIL. However, some reports have shown ZFS with a ZIL to be faster than using non-volatile cache. You should test performance using your workload. > Is it worth tweaking zfs_nocacheflush or zfs_vdev_max_pending? As I mentioned above, if the MDS has a non-volatile cache, then setting zfs_nocacheflush might help performance. If you're exporting one LUN per device then you shouldn't need to adjust the max_pending. If you're exporting larger RAID10 luns from the MDS, then increasing the value might help for read workloads. -B -- Brandon High : bh...@freaks.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
