Hi,
I'm reading a directory with 5.000.000 files (2,4 GB) inside a
guest using "find | grep -c".
On the host I saw high write IO (40 MB/s !) during over 1 hour
using virt-top.
I later repeated the read-only operation inside the guest and no
additional data was written on the host. The operation took only
some seconds.
I believe QEMU was creating some kind of cache or metadata map the first time I accessed the inodes.
But I wonder why the cache or metadata map wasn't available the first time and why QEMU had to recreate it?
The VM has "compressed base <- snap 1" and base was converted without prealloc.
Is it because we created the base using convert without metadata prealloc and so the metadata map got lost?
I will do some experiments soon using convert + metadata prealloc
and probably find out myself, but I will happy to read your
comments and gain some additional insights.
If it the problem persists, I would try again without compression.
Additional info: