zfs as layer distributor
andrew at modulus.org
Mon Oct 6 00:02:09 UTC 2008
Dimitar Vasilev wrote:
> Hi all,
> Does someone use zfs as layer distributor on the top of hardware raid -
I've found ZFS works faster when given more than one disk device. The
reason being, it is smart about writing journal logs and metadata copies
to different devices, resulting in higher performance by using idle
disks. It also provides more "channels" for write clustering so higher
throughput on write-heavy loads.
Secondly if you use ZFS to provide RAID1 or RAID5, due to checksumming
it can be smarter about which data it chooses in the event of a checksum
failure. Hardware RAID can only do this with RAID6.
Finally, when ZFS issues "flush cache" command to the disk for metadata
and journal logs, there is less data to flush when you give it multiple
smaller devices. If you have a single monolithic RAID device with a
large (eg. 256mb) cache, it can ruin performance while the RAID card
flushes its entire cache. (This can be disabled with a sysctl).
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