> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of P-O Yliniemi > > * Using a separate disk for logging might give problems if the log > device goes wrong. To avoid this - keep the log on the disk pool, or > mirror the log device.
Just a couple of corrections here: You wouldn't use a non-redundant disk in your pool, would you? So don't use a non-redundant log device either. It's nothing special to log devices. But yes, it's true, "using a separate disk for log might give problems if the log device goes wrong." Just like any other device (except cache). And even this is false in later versions of zpool. In later versions of zpool, under most conditions, failing unmirrored log devices result in no harm, and even in the worst conditions, result only in max 30sec data loss, not whole-pool loss. And the conclusion is: (a) don't use a dedicated log device, or (b) use a dedicated log device, but make sure it's mirrored > * A SSD drive as a log device would increase read speed over network > based sharing protocols (NFS or SMB, which will be used at the location > of this server) SSD log device is used for sync writes only. Will not affect read speed. Perhaps you're thinking of cache devices, which can sometimes increase read speeds. > * Disk performance increased by adding SSD cache and log devices will > die out (to a speed slower than the spindle disks) when the log and > cache disks once have been filled up to its maximum capacity. So the > use > of SSD disks for cache and log is a waste of money and drive bays. Disagree wholeheartedly. Even if it's true that the SSD has to suffer the penalty of read-modify-write (which is a questionable assertion) you're still comparing 3 operations of a 8,000 IOPS device, versus 1 operation on a 200 IOPS device. Even with this penalty (which is sometimes phantom) it's still an order of magnitude performance gained. > * Use DDR-based drives like DDRDrive (or i-RAM ?) for ZIL Best performance this way, true. But it's not necessarily a solution for everyone. > I am still able to reorganize the use of the SSD disks (reinstall > OpenSolaris), and even replace any one of them with 2.5" spindle disks, > so any more suggestions are highly welcome. You don't need to reinstall osol. Just replace those drives with some other drives. And make sure you understand how to do that ... formatting, fdisk, partition, slice, and grub. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
