I hope the data your running the CEPH server isn't important if your looking to
run a Cache tier with just 2 SSDS / Replication of 2.
If your cache tier fails, you basically corrupt most data on the pool below.
Also as Wido said, as much as you may get it to work, I don't think it will
give you the performance you expected, can you not create a separate small SSD
pool as a scratch disk for the VM's for when they are doing heavy temp I/O?
Leaving your current data and setup untouched.
---- On Mon, 16 Sep 2019 18:21:47 +0800 Eikermann, Robert
<mailto:[email protected]> wrote ----
We have terrible IO performance when multiple VMs do some file IO. Mainly do
some java compilation on that servers. If we have 2 parallel jobs everything is
fine, but having 10 jobs we see the warning
“HEALTH_WARN X requests are blocked > 32 sec; Y osds have slow requests”. I
have two enterprise SSDs which gained good results in ceph tested with fio.
They are too small to have a separate “ssd_vms” pool and advertise it in
openstack as a separate storage
backend
--
-----------------------------------------------------------------
Robert Eikermann M.Sc.RWTH | Software Engineering
Lehrstuhl für Software Engineering | RWTH Aachen University
Ahornstr. 55, 52074 Aachen, Germany | http://www.se-rwth.de/
Phone ++49 241 80-21306 / Fax -22218 |
Von: Wido den Hollander [mailto:mailto:[email protected]]
Gesendet: Montag, 16. September 2019 11:52
An: Eikermann, Robert <mailto:[email protected]>; mailto:[email protected]
Betreff: Re: [ceph-users] Activate Cache Tier on Running Pools
On 9/16/19 11:36 AM, Eikermann, Robert wrote:
Hi,
I’m using Ceph in combination with Openstack. For the “VMs” Pool I’d like to
enable writeback caching tier, like described here:
https://docs.ceph.com/docs/luminous/rados/operations/cache-tiering/ .
Can you explain why? The cache tiering has some serious flaws and can even
decrease performance instead of improve it.
What are you trying to solve?
Wido
Should it be possible to do that on a running pool? I tried to do so and
immediately all VMs (Linux Ubuntu OS) running on Ceph disks got readonly
filesystems. No errors were shown in ceph (but also no traffic arrived
after enabling the cache tier). Removing the cache tier , rebooting the VMs
and doing a filesystemcheck repaired everything.
Best
Robert
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