Nicolas Williams wrote
> There have been threads about adding a feature to support slow mirror
> devices that don't stay synced synchronously. At least IIRC. That
> would help. But then, if the pool is busy writing then your slow ZIL
> mirrors would generally be out of sync, thus being of no help in the
> even of a power failure given fast slog devices that don't
> survive power
> failure.
I wonder if an AVS-replicated storage device on the backends would be
appropriate?
write -> ZFS-mirrored slog -> ramdisk -AVS-> physical disk
\
+-iscsi-> ramdisk -AVS-> physical disk
You'd get the continuous replication of the ramdisk to physical drive (and
perhaps automagic recovery on reboot) but not pay the syncronous write to
remote physical disk penalty
>
> Also, using remote devices for a ZIL may defeat the purpose of fast
> ZILs, even if the actual devices are fast, because what really matters
> here is latency, and the farther the device, the higher the latency.
A .5-ms RTT on an ethernet link to the iSCSI disk may be faster than a 9-ms
latency on physical media.
There was a time when it was better to place workstations' swap files on the
far side of a 100Mbps ethernet link rather than using the local spinning rust.
Ah, the good old days...
--Joe
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