PVEPERF: Low FYSNCS/SECOND on striped LV on LVM

[deranjer]

Question on performance

I was getting high IO times on my single HDD disk so starting looking into speeding things up.

I realized the drive I was using was pretty old, and was using SATA II.

I found two SATAIII 256GB drives and hooked them up, and created a NEW LVM with those drives and created a VG on it called pve_stripe.

I created a striped LV on that and called it "data" and the copied the current /var/lib/vz data onto it. I then unmounted the old /pve/data device and mounted the new /pve_stripe/data device on /var/lib/vz

Block size:

#blockdev --getbsz /dev/pve_stripe/data
4096

My fstab:

/dev/pve/root / ext4 errors=remount-ro 0 1
/dev/pve_stripe/data /var/lib/vz ext4 defaults 0 1
/dev/pve_stripe/swap none swap sw 0 0
proc /proc proc defaults 0 0

Now I have "swap" and "data" on the pve_strip VG, and my buffered reads are better than they were.

root@pve:~# pveperf /var/lib/vz
CPU BOGOMIPS: 56001.20
REGEX/SECOND: 1698144
HD SIZE: 393.60 GB (/dev/mapper/pve_stripe-data)
BUFFERED READS: 244.28 MB/sec
AVERAGE SEEK TIME: 15.46 ms
FSYNCS/SECOND: 52.98
DNS EXT: 85.53 ms
DNS INT: 66.31 ms

However, my FYNCS/SECOND are extremely low. Is there any way to get my FSYNC speed up? When just running 3 of my lxc containers on "normal" load, I have an IO delay of about 15-20%. I assume this is because of the FSYNCS?

 

[snowman66]

AFAIK this is because of ext4 (barrier vs nobarrier). But someone with more experience can tell more...

https://forum.proxmox.com/threads/ext4-or-not-ext4-mount-options.20285/#post-103475

 

[deranjer]

Well, nobody on that link seems to have a firm answer to this. Not sure how to proceed on this.