On Sat, Dec 06, 2014 at 11:46:29PM +0000, James Harper wrote:
ps: performance on a zfs pool is notably improved (especially for random writes) if you have a small (4 or 8GB is plenty) SSD partition as a zfs log device.
But make sure your SSD partition is itself in a RAID of some sort too :)
not necessarily. redundancy in the ZIL is good, but can be achieved simply by having two ZIL devices. in fact, it's better to do it this way than to use a raid device - zfs works much better if it has direct knowledge and control of all devices in the pool. in particular, you should never give a raid array to zfs. instead, give the individual drives in the array to zfs and use zfs to construct the raid, otherwise you'll lose most of the benefit of using zfs (including zfs' ability to repair data corruption) see http://en.wikipedia.org/wiki/ZFS#ZFS_and_hardware_RAID e.g. i have two SSDs in my main system, partitioned to provide an mdadm raid1 mirror for my rootfs (170GB), mdadm raid1 /boot (1GB), two swap partitions, two non-raid ZIL partitions (4GB each), and two non-raid zfs l2arc cache partitions (50GB each). it's not a perfect setup - if money was irrelevant, i would have separate devices for root+boot, zil, and l2arc....but it's a reasonable compromise on speed, redundancy, and cost. i'd also need at least another 4 SATA ports if i had them on separate devices. my zpools (two of them, one for daily use and one as a backup pool for all systems on my network) are separate drives on an IBM M1015 SAS controller (around $100 for 8 ports which can handle SAS or SATA drives). i have a similar setup on my mythtv box, which also has a zpool for bulk storage but only a single SSD for root, /boot, zil, and l2arc cache. craig -- craig sanders <cas@taz.net.au>