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Re: [linux-lvm] Testing the new LVM cache feature



On Thu, May 29, 2014 at 05:06:48PM -0400, Mike Snitzer wrote:
> On Thu, May 29 2014 at  4:47pm -0400,
> Richard W.M. Jones <rjones redhat com> wrote:
> > To be clear, that means I should do:
> > 
> > lvcreate -L 1G -n lv_cache_meta vg_guests /dev/fast
> > lvcreate -L 229G -n lv_cache vg_guests /dev/fast
> > lvconvert --type cache-pool --poolmetadata vg_guests/lv_cache_meta vg_guests/lv_cache
> > blkdiscard /dev/vg_guests/lv_cache
> > lvconvert --type cache --cachepool vg_guests/lv_cache vg_guests/testoriginlv
> > 
> > Or should I do the blkdiscard earlier?
> 
> You want to discard the cached device before you run fio against it.
> I'm not completely sure what cache-pool vs cache is.  But it looks like
> you'd want to run the discard against the /dev/vg_guests/testoriginlv
> (assuming it was converted to use the 'cache' DM target, 'dmsetup table
> vg_guests-testoriginlv' should confirm as much).

I'm concerned that would delete all the data on the origin LV ...

My origin LV now has a slightly different name.  Here are the
device-mapper tables:

$ sudo dmsetup table
vg_guests-lv_cache_cdata: 0 419430400 linear 8:33 2099200
vg_guests-lv_cache_cmeta: 0 2097152 linear 8:33 2048
vg_guests-home: 0 209715200 linear 9:127 2048
vg_guests-libvirt--images: 0 1677721600 cache 253:1 253:0 253:2 128 0 default 0
vg_guests-libvirt--images_corig: 0 1677721600 linear 9:127 2055211008

So it does look as if my origin LV (vg_guests/libvirt-images) does use
the 'cache' target.

Rich.

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