[ovirt-users] oVirt Node with bcache

[Yaniv Kaul]

On Wed, Aug 16, 2017 at 4:37 PM, FERNANDO FREDIANI <
fernando.frediani at upx.com> wrote:

> Hello
>
> I just wanted to share a scenario with you and perhaps exchange more
> information with other people that may also have a similar scenario.
>
> For a couple of months I have been running a oVirt Node (CentOS 7.3
> Minimal) with bcache (https://bcache.evilpiepirate.org/) for caching a
> SSD with HDD disks. The setup is simple and was made for a prof of concept
> and since them has been working better than expected.
> This is a standalone host with 4 disks being: 1 for Operating System, 2 x
> 2TB 7200 RPM in software RAID 1 and 1 x PCI-E NVMe 400GB SSD which plays
> the caching device for both reads and writes. The VM storage folder is
> mounted as a ext4 partition on the logical device created by bcache
> (/dev/bcache0). All this is transparent to oVirt as all it sees is a
> /folder to put the VMs.
>
> We monitor the IOPS on all block devices individually and see the behavior
> exactly as expected: random writes are all done on the SSD first and them
> streamed sequentially to the mechanical drives with pretty impressive
> performance. Also in the beginning while the total amount of data was less
> than 400GB ALL read used to come from the caching device and therefore
> didn't use IOPS from the mechanical drives leaving it free to do basically
> writes. Finally at sequential IOPS (as described by bcache) are
> intelligently passed directly to the mechanical drives (but they are not
> much).
>
> Although bcache is present on kernel 3.10 I had to use kernel-ml 4.12
> (from Elrepo) and I had also to compile the bcache-tools as I could not
> find it available in any repository.
>

Nice!
It'd be great if you could write an ovirt.org blog about setting it up and
how it worked for you in.
Have you considered using dm-cache?
Y.


>
> Regards
> Fernando
>
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