[linux-lvm] Strange dm-cache activity at startup

[Zdenek Kabelac]

Dne 10.9.2015 v 11:30 Stefan Ring napsal(a):
> I have a fairly simple dm-cache setup with one PV on an HDD partition
> as the origin block device, and the cache LVs live on a partition on
> an SSD. The cache is in writethrough mode. Since I have no prior
> experience with this, I basically followed the lvmcache man page when
> creating this setup a few months ago.
>
> Every morning at startup, the system immediately starts prolonged
> activity on the devices involved in the cache setup. iostat shows
> reading activity from the cache device and constant write activity on
> the HDD. The HDD is fully utilized, and this goes on for more than an
> hour. After that, everything goes into what I would consider the
> "normal" state with only the IO activity going on that I actively
> throw at it.
>
> Is this normal/expected? What does it do? Why does it write back huge
> amounts of data to the HDD after each system start?
>
> Kernel is currently 3.17.8-200.fc20.x86_64 (Fedora)
> Userland has been upgraded to fc22 meanwhile

Please first try to use the latest kernel.
Kernel 3.17 is almost a year old.

Lots of optimizations went in meanwhile.
It's pointless to hunt already fixed bug.

Zdenek