suspend writes for external snapshot
robert at mhi-tx.com
Thu Apr 27 14:13:35 UTC 2006
Eric Anderson wrote:
> Kris Kennaway wrote:
>> On Wed, Apr 26, 2006 at 04:07:32PM -0500, Robert wrote:
>>> I am trying to determine if there is a way to suspend write activity
>>> on a FreeBSD filesystem (currently 6.0R) in order to take a snapshot
>>> with external SAN software (Falconstor IPStor)?
>> Use a FreeBSD snapshot and then image that?
> He can't do it that way because the Falconstor is a raw block device and
> has no idea the difference between a snapshot and other filesystem bits.
> Robert - we have some very alpha patches in house that allow suspension
> of UFS filesystems for things like this (also working on online UFS
> growing). I'm not sure how close we really are to letting it loose in
> the wild, but we will definitely be making all the patches available to
> whomever wants it.
Sounds great thank you, I will keep an eye out for the patches.
I am still unclear as to the necessity of suspending writes based on the
following information from http://www.mckusick.com/softdep/
"By ensuring that the only inconsistencies are unclaimed blocks or
inodes, soft updates can eliminate the need to run a filesystem check
program after every system crash. Instead, the system is brought up
When it is convenient, a snapshot is taken and a background task can be
run on on that snapshot to reclaim any lost blocks and inodes. The use
of a snapshot allows normal filesystem activity to continue concurrently. "
Does this mean that I can take a snapshot of an in use filesystem and
the only ill effects will be the lost blocks and inodes which can be
reclaimed with background fsck once the snapshot is booted?
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