On Oct 20, 2009, at 10:24 PM, Frédéric VANNIERE wrote:
The ZIL is a write-only log that is only read after a power failure.
Several GB is large enough for most workloads.
You can't use the Intel X25-E because it has a 32 or 64 MB volatile
cache that can't be disabled neither flushed by ZFS.
I am surprised by this assertion and cannot find any confirmation from
Rather, the cache flush command is specifically mentioned as supported
Section 6.1.1 of the Intel X25-E SATA Solid State Drive Product Manual.
I suspect that this is confusion relating to the various file systems,
or virtualization platforms which may or may not by default ignore cache
Since NTFS uses the cache flush commands, I would be very surprised if
Intel would intentionally ignore it.
Imagine your server has a power failure while writing data to the
pool. In normal situation, with ZIL on a reliable device, ZFS will
read the ZIL and come back to a stable state at reboot. You may have
lost some data (30 seconds) but the zpool works. With the Intel
X25-E as ZIL some log data has been lost with the power failure
(32/64MB max) which lead to a corrupted log and so ... you loose
your zpool and all your data !!
The ZIL works fine for devices which support the cache flush command.
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