[dm-devel] Significantly dropped dm-cache performance in 4.13 compared to 4.11

[Stefan Ring]

On Tue, Nov 14, 2017 at 12:00 PM, Joe Thornber <thornber at redhat.com> wrote:
>
> I'm not sure what's going on here.  Would you mind sending me the
> metadata please?  Either a cache_dump of it, or a copy of the metadata
> dev?

I'd like to create a cache dump, but I'm not very experienced with
this stuff. I do:

$ cache_dump /dev/vg_zfs/lv_zfsdisk |less
syscall 'open' failed: Device or resource busy
Note: you cannot run this tool with these options on live metadata.

Which is what I feared/expected. However, after doing

$ lvchange -an vg_zfs/lv_zfsdisk

the device disappears, and I cannot run cache_dump on it as well. So
how do I make it not live, while still visible?