On 4/29/22 5:17 AM, Vladimir Brik wrote:
Some new information:
It looks like the hang happens at the 4194304 byte boundary. For example:
`dd if=/dev/zero of=zero bs=4194304 count=1` succeeds, but
`dd if=/dev/zero of=zero bs=4194305 count=1` hangs with an empty file.
If bs is set lower, e.g. 8192, then 4194304 bytes are written to a
file and then the hang happens. The problem is transient. Sometimes it
goes away sometimes it comes back. Tested on 3.10.0-1160.62.1.el7 kernel.
Test this again by using the upstream kernel, still couldn't reproduce
it. It seems only exists in old kernel and has been fixed by some commits.
-- Xiubo
I've resolved slow metadata io issues and metadata is now stored on 12
NVMe flash OSDs, so that wasn't the cause.
Vlad
On 4/24/22 16:25, Vladimir Brik wrote:
Hello
We are experiencing an issue where, sometimes, when users write to
cephfs an empty file is created and then the application hangs,
seemingly indefinitely. I am sometimes able to reproduce with dd.
Does anybody know what might be going on?
Some details:
- ceph health complains about 100+ slow metadata IOs
- CPU utilization of ceph-mds is low
- We have almost 200 kernel cephfs clients
- Cephfs metadata is stored on 3 OSDs that use NVMe flash AICs
Vlad
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