[sheepdog-users] Issues with gateway mode

[Hitoshi Mitake]

On Mon, Nov 9, 2015 at 2:43 PM, Gerald Richter <richter at ecos.de> wrote:
> Hi Hitoshi,
>
> as long as the object cache doesn't work relieable my setup doesn't make
> sense, because of the slow network connections (only 200MBit/s).
>
> This will only work if most reads and writes are statisfied by the local
> object cache. If every read and write goes through the network, than
> performance will be very poor.

Could you provide benchmark results of both of the configurations
(with and without object cache)  on your environment?
Thanks,
Hitoshi

>
> At the moment I have only 2 storage nodes and 3 gateways with 6 VMs for
> testing (and object cache turned on). This works fine, but as you say that
> object cache should not be used, this setup will not scale (in the end there
> will be about 100 VMs on 8-10 nodes).
>
> I need something that allows me such a setup over slow network connections.
> This mean that must be some cacheing and an asynchronous write back. For the
> kind of VMs I am running it's ok, if some data is lost in case of failure.
>
> Sheepdog with object cache looked very promising for such a setup. I didn't
> found any other solution so far.
>
> Regards
>
> Gerald
>
>
> Am 09.11.2015 um 05:01 schrieb Hitoshi Mitake:
>
> Hi Gerald,
>
> On Sat, Nov 7, 2015 at 9:05 PM, Gerald Richter <richter at ecos.de> wrote:
>
> Hi,
>
> I need to setup a storage cluster over slow network connections.
>
> Sheepdog in gateway mode seems to be the ideal solution for me. That mean I
> have three or more storage nodes and a lot of gateway node that only uses
> the sheepdog cache. As long as most request are statisfied by the cache
> (which is an ssd), performance should be ok. Slow network connection aren't
> a problem as long as the cache uses write back mode.
>
> I have setup a test environment with 0.9.2 . As long as the vm are small
> enough to fit completly in the cache it seems to work, but when the vm is
> bigger than the cache I get I/O errors after some time. Also after a reboot
> of the host machine it seems to take very long time, until I can boot the
> vm, also the cache is still uptodate.
>
> Browseing through the mailing list archive I found
> http://lists.wpkg.org/pipermail/sheepdog-users/2015-August/015120.html,
> where Hitoshi said "object cache is not maintained currently. Please do not
> use it.". Is this still true? or is there any way to use the setup I
> described above?
>
> Yes, it's true. Please don't use object cache.
>
> BTW, many gateways + fewer storage nodes is dangerous. Because the
> gateways doesn't contribute to increasing parallelism of disk I/O. If
> a number of VMs and storage nodes are unbalanced, performance of
> virtual disks will be very bad. Could you provide a detailed number of
> VMs, gateway nodes, and storage nodes?
>
> Thanks,
> Hitoshi
>
> Thanks & Regards
>
> Gerald
>
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