[Ocfs2-users] OCFS2 Snapshotting, freezing, monitoring block device

[Michael Moody]

Dear Mailing List,

(I was gonna start with Dear Diary but alas).

I have a few questions about freeze/thaw operations, block devices, etc.

Currently, I know that there is a patch to allow freeze/thaw operations, 
as it was requested by NetApp. This is good. Let's assume for a moment 
that you weren't using a SAN or something of that nature, but were able 
to develop a software that could do a "software snapshot" (I know of at 
least one of these, r1soft.com's CDP, and also Volume Shadow Copy for 
windows does the same). Most of these softwares work by monitoring the 
block device for changes after an operation like this: (psuedo code)

freeze_bdev(/dev/sdb1) //sync write caches to disk, etc
take_snapshot(/dev/sdb1) //consistent point in time
monitor_bdev(/dev/sdb1) //watch at the kernel level for writes/changes 
to the block device, and keep in memory what the area of disk was before 
if it's marked as needing to be changed, monitoring continues during the 
entire backup process, even after the thaw
thaw_bdev //allow writes to disk to resume

If you were to monitor the block device on an ocfs2 volume, would you 
see the changes from the other nodes? How exactly would one be able to 
accomplish the above?

Any chance of snapshotting support, or some "online backup" support 
making it's way into ocfs2 anytime in the near future? rsync has it's 
limits.

Thanks,
Michael

-- 

Michael S. Moody
Sr. Systems Engineer
Global Systems Consulting
Direct: (650) 265-4154
Web: http://www.GlobalSystemsConsulting.com

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