[linux-lvm] Removing a snapshot under heavy IO causes LVM hangs

Steffen Plotner swplotner at amherst.edu
Fri Nov 11 04:53:59 UTC 2005


I have found 2 scenarios using FC4 (2.6.13-latest) that cause LVM problems:
700GB volume, create a snapshot of 100Gb, copy the snap to another disk, remove the snapshot. The snapshot remove never ends it just hangs. One can type lvscan, it will display a few LVs and then hang, press Ctrl-C to get out of that. Ctrl-C does not work with lvremove. No /var/log/messages indicating cause.
We believe this might happen because the volume copy takes about 8hours, however if I do a snap and then instantly remove it, it works fine. The 8 hour time frame + plus moderate IO appears to be the problem.
Labtest: create a 20G volume, create a 8G snap. From another terminal do dd if=/dev/zero of=/dev/vg/lv bs=1M, after running for a few minutes remove the snapshot - it cannot be removed until ALL IO ceases on the original volume.
I have tried the development FC4 2.6.14 kernel today and that causes the same problems. lvm2 tools: lvm2-2.01.08-2.1
Steffen Plotner 
Systems Administrator/Programmer 
Systems & Networking 
Amherst College 
PO BOX 5000 
Amherst, MA 01002-5000 
Tel (413) 542-2348 
Fax (413) 542-2626 
Email: swplotner at amherst.edu 
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