which hdd driver inside VM to choose

[chalan]

i have done some test inside my VM (ftp/samba/fileserver)

root@pve-klenova:~# arcstat
time read miss miss% dmis dm% pmis pm% mmis mm% arcsz c
21:42:44 0 0 0 0 0 0 0 0 0 2.0G 2.0G

hdd driver test inside this VM

root@merkur:~# uname -a
Linux merkur 4.4.0-101-generic #124-Ubuntu SMP Fri Nov 10 18:29:59 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

root@merkur:~# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial

scsi2, local, qcow2, cache=writethrough, size=10G

write:
root@merkur:~# dd if=/dev/zero of=/mnt/sdc/temp.raw bs=1024k count=4096 && rm /mnt/sdc/temp.raw
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 39.9517 s, 108 MB/s

read:
/dev/sdc:
Timing cached reads: 3232 MB in 2.00 seconds = 1616.37 MB/sec
Timing buffered disk reads: 2228 MB in 3.00 seconds = 742.12 MB/sec

scsi3, local-zfs, zvol, cache=writethrough, size=10G

write:
root@merkur:~# dd if=/dev/zero of=/mnt/sdd/temp.raw bs=1024k count=4096 && rm /mnt/sdd/temp.raw
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 95.2488 s, 45.1 MB/s

read:
/dev/sdd:
Timing cached reads: 3160 MB in 2.00 seconds = 1579.77 MB/sec
Timing buffered disk reads: 1724 MB in 3.00 seconds = 574.15 MB/sec

virtio3, qcow2, cache=writethrough, size=10G

write:
root@merkur:~# dd if=/dev/zero of=/mnt/vdb/temp.raw bs=1024k count=4096 && rm /mnt/vdb/temp.raw
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 11.2733 s, 381 MB/s

read:
/dev/vdb:
Timing cached reads: 3176 MB in 2.00 seconds = 1588.04 MB/sec
Timing buffered disk reads: 2364 MB in 3.00 seconds = 787.76 MB/sec

virtio4, local-zfs, zvol, cache=writethrough, size=10G

write:
root@merkur:~# dd if=/dev/zero of=/mnt/vdc/temp.raw bs=1024k count=4096 && rm /mnt/vdc/temp.raw
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 54.6697 s, 78.6 MB/s

read:
/dev/vdc:
Timing cached reads: 3136 MB in 2.00 seconds = 1567.85 MB/sec
Timing buffered disk reads: 1620 MB in 3.00 seconds = 539.48 MB/sec

1. which driver i have to use
2. local qcow2 or local-zfs zvol?
3. local-zfs zvol is the default, does it mean that local qcow2 is not recomended? why?
   
4. are the write speeds 381 MB/s with qcow2 and virtio driver, realy HDD speeds or some kind of cache?

thank you....

 

[wolfgang]

Hi,

which driver i have to use

We recommend SCSI with Virto bus, because it has the most development at the moment.

local qcow2 or local-zfs zvol?

on a ZFS backend storage local-zfs.

local-zfs zvol is the default, does it mean that local qcow2 is not recomended? why?

Yes, is is not recommended because qcow and zfs are both copy on write systems, so you will write for one write 4 times.

are the write speeds 381 MB/s with qcow2 and virtio driver, realy HDD speeds or some kind of cache?

With this information, you can tell.
But when you write on ZFS there is a hight change a cache is involved.