Specifying them to be the same device is redundant and not necessary. They will be put on the bluestore device by default unless you specify them to go to another device.
On Fri, Aug 18, 2017 at 9:17 AM Hervé Ballans <herve.ballans@xxxxxxxxxxxxx> wrote:
Le 16/08/2017 à 16:19, David Turner a écrit :
Would reads and writes to the SSD on another server be faster than reads and writes to HDD on the local server? If the answer is no, then even if this was possible it would be worse than just putting your WAL and DB on the same HDD locally. I don't think this is a use case the devs planned for.
You can definitely put multiple WAL land DB partitions on a single SSD.
Thanks David for your reply.
Indeed, I have no idea if I/O operations on a distant SSD are faster than on a local HDD ?..I thought naively that in the case of a 10Gbs network, the speed of the bandwidth was always higher than that of the disk, whatever its technology, but it's true that many other factors come into play (in any case, it's an interesting problem, if I have time, I will try to do some benchmarks...)
In relation to your answer, I have another question please, in the case of an OSDs server composed only with HDD disks, what is the best practice : just configure each OSD as a single BlueStore storage device or add on each disk both WAL and DB devices (e.g. ceph-disk prepare --bluestore /dev/sdd --block.wal /dev/sdd --block.db /dev/sdd) ?
I ask this because the online documentation on "BlueStore Config Reference" states that adding these devices are useful only if the device used is faster than the primary device ?
Thanks again,
Hervé
_______________________________________________
On Wed, Aug 16, 2017, 6:04 AM Hervé Ballans <herve.ballans@xxxxxxxxxxxxx> wrote:
Hi,
We are currently running two Proxmox/ceph clusters that work perfectly
(since 2014) and thank to this succesful experience, we plan to install
a new Ceph cluster for storage of our computing cluster.
Until now, we only used RBD (virtualization context) but now we want to
use CephFS for this new cluster (separated from the other two, hardware
is different and dedicated for this new clusters).
I'm interested in testing a CephFS cluster with BlueStore as a backend
storage.
I have several OSDs servers (with a dozen SATA HDDs on each) but some do
not have an additional SSD disk (only 3 of the servers have an
additional SSD).
My question is about BlueStore WAL/DB devices. When I read the
documentation, it seems that adding both WAL and DB devices improve
BlueStore performances.
But, can we configure these devices on a distant SSD (I mean on a SSD
which is not on the local OSDs server but on an another machine which is
on the same Ceph cluster) ?
If yes, can I configure mulitple WAL or DB devices on the same SSD ?
And finally, is it relevant to do that (I mean in term of performance) ?
Hoping to have been clear on my context, thanks in advance for your
reply or your reflection.
Regards,
Hervé
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