On 2014-02-18 13:04, Udo Grabowski (IMK) wrote:
On 18/02/2014 12:27, Hans J. Albertsson wrote:
1. Is it really worthwhile to mirror an SSD-based ZIL & L2ARC cache, if
the SSD has proper power loss protection??
SSD logs no longer need to be mirrors, in case of a loss you
can now simply delete them. But if you loose the SSD when the
server panics or reboots, you can loose some TXGs, so if you
want absolute data consistency, a mirror is still a good idea.
With the old OSOL 2009.06, you could not import filesystems with
logs that were broken, so a mirror was mandatory for a log device.
Yes, and also you don't mirror L2ARC, you effectively stripe it :)
As for mirroring... devices do die. SSDs might wear out and die
suddenly, perhaps faster than HDDs though this depends on your
usage patterns and the device's engineering tradeoffs.
If you make a cronjob to send off the zfs-auto-snapshots from
your rpool onto the data pool for example (and take care to
avoid auto-mounting these copies) then in case of rpool death
you can boot up from a live media and copy back your rpool
backup onto a new SSD.
A list member (Udo?) installed onto a separate 4-way-mirrored
rpool made from small partitions on the data disks; in your
case this would leave the SSD available for only caches and
not as critical a component when/if it dies. So this is also
an option to consider...
Good luck,
//Jim
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