Gregory Shaw wrote:
I had a question to the group:
In the different ZFS discussions in zfs-discuss, I've seen a
recurring theme of disabling write cache on disks. I would think that
the performance increase of using write cache would be an advantage, and
that write cache should be enabled.
Realistically, I can see only one situation where write cache would
be an issue. If there is no way to flush the write cache, it would be
possible for corruption to occur due to a power loss.
There are two failure modes associated with disk write caches:
1) the disk write cache for performance reasons doesn't write back
data (to diff. blocks) to the platter in the order they were
received, so transactional ordering isn't maintained and
corruption can occur.
2) writes to different can disks have different caching policies, so
transactions to files on different filesystems may not complete
correctly during a power failure.
ZFS enables the write cache and flushes it when committing transaction
groups; this insures that all of a transaction group appears or does
not appear on disk.
- Bart
--
Bart Smaalders Solaris Kernel Performance
[EMAIL PROTECTED] http://blogs.sun.com/barts
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