On 12/03/09 09:21, mbr wrote:
Hello,
Bob Friesenhahn wrote:
On Thu, 3 Dec 2009, mbr wrote:
What about the data that were on the ZILlog SSD at the time of
failure, is
a copy of the data still in the machines memory from where it can be
used
to put the transaction to the stable storage pool?
The intent log SSD is used as 'write only' unless the system reboots,
in which case it is used to support recovery. The system memory is
used as the write path in the normal case. Once the data is written
to the intent log, then the data is declared to be written as far as
higher level applications are concerned.
thank you Bob for the clarification.
So I don't need a mirrored ZILlog for security reasons, all the information
is still in memory and will be used from there by default if only the
ZILlog SSD fails.
Mirrored log devices are advised to improve reliablity. As previously mentioned,
if during writing a log device fails or is temporarily full then we use the
main pool
devices to chain the log blocks. If we get read errors when trying to replay the
intent log (after a crash/power fail) then the admin is given the option to
ignore
the log and continue or somehow fix the device (eg re-attach) and then retry.
Multiple log devices would provide extra reliability here.
We do not look in memory for the log records if we can't get the records
from the log blocks.
If the intent log SSD fails and the system spontaneously reboots, then
data may be lost.
I can live with the data loss as long as the machine comes up with the
faulty ZILlog SSD but otherwise without probs and with a clean zpool.
The log records are not required for consistency of the pool (it's not a
journal).
Has the following error no consequences?
Bug ID 6538021
Synopsis Need a way to force pool startup when zil cannot be replayed
State 3-Accepted (Yes, that is a problem)
Link
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6538021
Er that bug should probably be closed as a duplicate.
We now have this functionality.
Michael.
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