Re: Virtio-scsi and block mirroring
On Thu, Apr 14, 2022 at 16:36:38 +0000, Bjoern Teipel wrote:
Hello everyone,
Hi,
I’m looking at an issue where I do see guests freezing (Dl) process state during a block
disk mirror from one storage to another storage (NFS) where the network stack of the guest
can freeze for up to 10 seconds.
Looking at the storage and IO I noticed good throughput ad low latency <3ms and I am
having trouble to track down the source for the issue, as neither storage nor networking
show issues. Interestingly when I do the same test with virtio-blk I do not really see the
process freezes at the frequency or duration compared to virtio-scsi which seem to
indicate a client side rather than storage side problem.
Hmm, this is really weird if the difference is in the guest-facing
device frontend.
Since libvirt is merely setting up the block job for the copy and the
copy itself is handled by qemu I suggest you contact the
qemu-block(a)nongnu.org mailing list.
Unfortunately you didn't provide any information on the disk
configuration (the VM XML) or how you start the blockjob, which I could
translate for you into qemu specifics. If you provide such information I
can do that to ensure that the qemu folks have all the relevant
information.