[linux-lvm] Network-attached block storage and local SSDs for dm-cache
zkabelac at redhat.com
Tue Apr 23 10:20:13 UTC 2019
Dne 19. 04. 19 v 21:30 Konstantin Ryabitsev napsal(a):
> Hi, all:
> I know it's possible to set up dm-cache to combine network-attached block
> devices and local SSDs, but I'm having a hard time finding any first-hand
> evidence of this being done anywhere -- so I'm wondering if it's because there
> are reasons why this is a Bad Idea, or merely because there aren't many
> reasons for folks to do that.
> The reason why I'm trying to do it, in particular, is for mirrors.kernel.org
> systems where we already rely on dm-cache to combine large slow spinning disks
> with SSDs to a great advantage. Most hits on those systems are to the same set
> of files (latest distro package updates), so dm-cache hit-to-miss ratio is
> very advantageous. However, we need to build newest iterations of those
> systems, and being able to use network-attached storage at providers like
> Packet with local SSD drives would remove the need for us to purchase and host
> huge drive arrays.
> Thanks for any insights you may offer.
From lvm2 POV - if you put both devices into single VG - you should be able
to easily configure the setup in a way, that your 'main/origin' LV sitting on
network storage and cache is setup to be located on SSD.
lvcreate -LMAXSIZE --name MYLV vg /dev/networkshdd
lvcreate --cache -Lcachesize vg/MYLV /dev/ssd
But of course as Mike points out - cache currently expects the origin device
is reliable one.
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