On Thu 27 Aug 2020 06:29:15 PM CEST, Yoonho Park wrote:
> Below is the data with the cache disabled ("virsh attach-disk ... --cache
> none"). I added the previous data for reference. Overall, random read
> performance was not affected significantly. This makes sense because a
> cache is probably not going to help random read performance much. BTW how
> big the cache is by default? Random write performance for 4K blocks seems
> more "sane" now. Random write performance for 64K blocks is interesting
> because base image (0 overlay) performance is 2X slower than 1-5 overlays.
> We believe this is because the random writes to an overlay actually turn
> into sequential writes (appends to the overlay). Does this make sense?
>
>
> NO CACHE
>
> 4K blocks 64K blocks
>
> olays rd bw rd iops wr bw wr iops rd bw rd iops wr bw wr iops
>
> 0 4478 1119 4684 1171 57001 890 42050 657
>
> 1 4490 1122 2503 625 56656 885 93483 1460
I haven't been able to reproduce this (I tried the scenarios with 0 and
1 overlays), did you figure out anything new or what's the situation?
Berto
