Very low fsync by pveperf

[Tapio Lehtonen]

I tested pveperf on OVH Mini HG host:

Base Board Information
Manufacturer: Intel Corporation
Product Name: S2600CW
root@rauta:~# lspci | grep SATA
00:11.4 SATA controller: Intel Corporation C610/X99 series chipset sSATA Controller [AHCI mode] (rev 05)
00:1f.2 SATA controller: Intel Corporation C610/X99 series chipset 6-Port SATA Controller [AHCI mode] (rev 05)
root@rauta:~#


root@rauta:~# fdisk -l

Disk /dev/sda: 3.7 TiB, 4000787030016 bytes, 7814037168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 4ECA49F1-C4D9-48C8-A64D-99F9BB47838E

Device Start End Sectors Size Type
/dev/sda1 40 2048 2009 1004.5K BIOS boot
/dev/sda2 4096 40962047 40957952 19.5G Linux RAID
/dev/sda3 40962048 43057151 2095104 1023M Linux RAID
/dev/sda4 43057152 7814027263 7770970112 3.6T Linux RAID

Disk /dev/sdb: 3.7 TiB, 4000787030016 bytes, 7814037168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 44B82AAA-AA4B-4F1C-AEEF-DC8810EC79EC

Device Start End Sectors Size Type
/dev/sdb1 40 2048 2009 1004.5K BIOS boot
/dev/sdb2 4096 40962047 40957952 19.5G Linux RAID
/dev/sdb3 40962048 43057151 2095104 1023M Linux swap
/dev/sdb4 43057152 7814027263 7770970112 3.6T Linux RAID

Disk /dev/md2: 19.5 GiB, 20970405888 bytes, 40957824 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/md4: 3.6 TiB, 3978736631808 bytes, 7770969984 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/pve-data: 3.6 TiB, 3974438584320 bytes, 7762575360 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
root@rauta:~#

root@rauta:~# pveperf /var/lib/vz
CPU BOGOMIPS: 76618.72
REGEX/SECOND: 2049752
HD SIZE: 3643.28 GB (/dev/mapper/pve-data)
BUFFERED READS: 174.97 MB/sec
AVERAGE SEEK TIME: 21.24 ms
FSYNCS/SECOND: 16.89
DNS EXT: 176.51 ms
DNS INT: 22.54 ms (rauta)
root@rauta:~#

This is proxmox
pve-manager/4.4-22/2728f613 (running kernel: 4.4.117-1-pve)

Installed from Proxmox image provided by OVH, so I assume it has the necessary drivers available. I believe this is a very plain installation, I did not change settings from default.

Why is FSYNC so low? I copied pveperf to my desktop and here it shows
FSYNCS/SECOND: 50.99
which is three times more than the OVH server.
Is my OVH setup somehow lacking something that would increase fsyncs/s ?

 

[udo]

Hi,
looks that ovh use software raid1 with two 4TB disks.
Without cache (BBU) such an setup is slow for synced writes.

Udo

 

[Tapio Lehtonen]

It is software RAID, yes. But why is it so very slow?

 

[Gustavo Spadari]

Hi.

Looking for some info about this problem, I came across this bug report: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1785020

Could this be related? I was looking some other thread refering this kernel problem that seems to be resolved since 4.18 and couldn't find anything.

Thanks.