[PVE-User] Slow speeds when KVM guest is on NFS

Mikhail m at plus-plus.su
Tue Nov 15 23:05:00 CET 2016

On 11/16/2016 12:43 AM, Brian :: wrote:
> What type of disk controller and what caching mode are you using? 

The storage server is built with 4 x 4TB ST4000NM0034 Seagate disks,
attached to LSI Logic SAS3008 controller. Then there's Debian Jessie
with software RAID10 using MDADM. This space is given to Proxmox host
via iSCSI + LVM via 10 gbit ethernet. There's 32GB of RAM in this
storage server, so almost all this RAM can be used for cache (nothing
else runs there).

I ran various tests on the storage server locally (created local LV,
formatted it to EXT4 and ran there various disk-intensive tasks such as
copying big files, etc). My average write speed to this MDADM raid10 /
LVM / Ext4 filesystem is about 70-80mb/s. I guess it should be much
faster then that, but I can't find out where's the bottleneck in this

# cat /proc/mdstat
Personalities : [raid10]
md0 : active raid10 sda2[0] sdd2[3] sdc2[2] sdb2[1]
      7811819520 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
      bitmap: 11/59 pages [44KB], 65536KB chunk

unused devices: <none>

# pvs
  PV         VG   Fmt  Attr PSize PFree
  /dev/md0   vg0  lvm2 a--  7.28t 1.28t


> On Tue, Nov 15, 2016 at 9:36 PM, Mikhail <m at plus-plus.su> wrote:
>> On 11/16/2016 12:33 AM, Brian :: wrote:
>>> 90.4 MB/s isn't that far off.
>> Hello,
>> Yes, but I'm only able to get these results when doing simple "dd" test
>> directly on Proxmox host machine inside NFS-mounted directory. KVM
>> guest's filesystem is not getting even 1/4 of that speed when it's disk
>> resides on the very same NFS (Debian installation from stock ISO takes
>> ~hour to copy first halt of it's files..)
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