Ceph slow mons & SD OS disks

[Julian Lliteras]

I have an issue related to slow mons reported by ceph. Aside of bluestore kind of disks, I have regular warnings about slow monitos except one host. I suspect that all these warnings are raised due to logs and data collected from ceph to OS disk "/var/lib","/var/log". Since OS disk are SD disks, have a lot of write latency and any writes to disk have a severe penalty in performance. The host with sata disks do not suffer from these warnings.

My question is. Can logs be moved to a ramdisk or disabled without disturbing normal operation of ceph?

Thanks in advance
Julian.

 

[aaron]

My question is. Can logs be moved to a ramdisk or disabled without disturbing normal operation of ceph?

I would not advise to do that because there is always the chance that you will need those logs at some point.

Since OS disk are SD disks

Do I understand you correctly, that you mean SD cards by that? If so, I urge you to move the system to something else because even without Ceph, PVE will log quite a bit to disk and SD cards or USB flash drives usually don't last long in such a use case.

 

[Julian Lliteras]

Indeed, I have SD cards in raid1 for OS. I would make use whole disk bays for ceph osd.

I know log files are important, and Proxmox is doing quite writes, proxmox not suffer penalty from this writes but ceph is very sensitive here. My question is if any last tuning option is available to minimize writes or use some sort of ramdisk/scripting

Anyway I'm care of using SD is not good idea, but without SD I would reduce 4 hosts x 2 disks of osds globally and reduce osd per host.

PD. A log server can be an efficient way to store al logs cluster wide!

Best regards.