* [linux-lvm] lvmcache comes back dirty after unclean shutdown
@ 2020-05-08 8:26 Paul Richards
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From: Paul Richards @ 2020-05-08 8:26 UTC (permalink / raw)
To: dm-devel, linux-lvm
I would like to add a warning to the lvmcache man page about its
suitability in environments that expect unclean shutdowns.
I've been using lvmcache on my laptop which has a small nvme drive and
a much larger hdd. I am using approx 60GiB of the nvme drive as a
cache for the 1TiB HDD.
With both "writethrough" and "writeback" modes an unclean shutdown
results in the entire cache being marked as dirty. On next boot the
system then spends a long time (4+ hours) writing the cache out to
disk. From what I can see this is known behavior of lvmcache ( and
). It's even documented in the kernel device mapper docs .
It seems to me that dm-cache and lvmcache are not appropriate for
environments that expect unclean shutdowns. In those environments I
have found bcache to be a bit more robust.
This is not a criticism of lvmcache and dm-cache. I am sure they
perform well in more robust environments. But I wonder if it would be
appropriate to add a warning note to the lvmcache man page about this
I am using Ubuntu 20.04 currently, if that's relevant, and I saw the
same issue with 18.04.
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