On 5/24/19 7:51 PM, Song Liu wrote:
On Fri, May 24, 2019 at 3:51 AM Michal Soltys <soltys@xxxxxxxx> wrote:
On 5/23/19 8:09 PM, Song Liu wrote:
Actually, this seems to be unreleated to underlying devices - the culprit seems to be attempting to write to an array after adding journal, without stopping and reassembling it first. Details below.
Thanks for these experiments. Your analysis makes perfect sense.
Do you think you can continue the experiments with the write journal before
this issue got fixed?
I am asking because this is not on the top of my list at this time. If
this is not
blocking other important tests, I would prefer to fix it at a later time.
Thanks,
Song
Yea it's fine. I can help with testing (whenever you sit down to this
issues) as well.
Question though - other than trying to add journal to existing live raid
- is this feature overall safe to use (or are there any other know
issues one should be aware of beforehand) ?
We (Facebook) have done some tests with it. However, we didn't put
it into production. The reason behind this decision was not reliability, but
performance concerns and high level directions. I think Redhat is
evaluating it.
Well I will give it a shot probably. My case scenario is that a bunch of
sync-happy VMs on top of lvm+raid seem to be crushing performance
(unless there are other reasons), even with very small disk usage.
Out of curiosity - is the journal in writeback mode controllable in some
way (e.g. frequency of how often it flushes to raid disks, whether it's
space or time (or both) based ?).
+ Xiao, who might be working on this.
Thanks,
Song
