Re: [Xen-users] Disk performance on guest incredibly low.

[Andy Smith <andy@xxxxxxxxxxxxxx>]

Hi,

On Sun, Dec 16, 2018 at 05:42:43PM +0100, frm@xxxxxxxxxxx wrote:
> At guest, I have:
> 
> `    dd if=/dev/zero of=a_file bs=1M count=1024 conv=fsync oflag=direct
>     1024+0 records in
>     1024+0 records out
>     1073741824 bytes (1.1 GB, 1.0 GiB) copied, 15.6421 s, 68.6 MB/s
> `
> 
> At Dom0 I have:
> 
> `    dd if=/dev/zero of=a_file bs=1M count=1024 conv=fsync oflag=direct
>     1024+0 records in
>     1024+0 records out
> 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 3.81855 s, 281 MB/s
> `

No ideas, sorry, but just for comparison:

guest:
$ dd if=/dev/zero of=a_file bs=1M count=1024 conv=fsync oflag=direct
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 2.51228 s, 427 MB/s

dom0:
$ dd if=/dev/zero of=/var/tmp/a_file bs=1M count=1024 conv=fsync oflag=direct
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 2.61745 s, 410 MB/s

PV guest, xen 4.10.3.

So yes it seems you are seeing something quite abnormal.

Cheers,
Andy

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