Slow disk speed on Guest VM

P

proteus

Member
Feb 24, 2021
27
17
23
I am new to Proxmox VE, I tried to find an answer for this problem with no luck.
The problem is that speed on Host is good but on Guest VM is very bad. I really tried all the cache types and 2 different ZFS Pools. The system specs are bellow for this test but i did tried on another Supermicro Server with AMD Epyc Rome and different HDD's with same results.


Test: Block 1M
fio --randrepeat=1 --ioengine=libaio --direct=0 --gtod_reduce=1 --name=test --filename=test --bs=1M --iodepth=32 --size=5G --readwrite=randrw --rwmixread=50 --numjobs=8 --time_based --runtime=120

### Quick Results
# HOST:
Run status group 0 (all jobs):
READ: bw=162MiB/s (170MB/s), 19.3MiB/s-20.8MiB/s (20.3MB/s-21.8MB/s), io=19.1GiB (20.5GB), run=120017-120819msec
WRITE: bw=164MiB/s (172MB/s), 19.7MiB/s-21.3MiB/s (20.7MB/s-22.4MB/s), io=19.3GiB (20.8GB), run=120017-120819msec


# Ubuntu 20.04 Guest VM / SCSI Controller: VirtIO SCSI / Default (No Cache) / Installed qemu-guest-agent
Run status group 0 (all jobs):
READ: bw=44.9MiB/s (47.1MB/s), 5062KiB/s-6190KiB/s (5184kB/s-6339kB/s), io=5496MiB (5763MB), run=120093-122414msec
WRITE: bw=46.0MiB/s (49.3MB/s), 5811KiB/s-6265KiB/s (5950kB/s-6416kB/s), io=5752MiB (6031MB), run=120093-122414msec



### This system is just for testing not production ###
DL380p G8 / P420i - HBA Mode
1 x HDD SATA 1TB Enteprise PVE Boot + 1 x USB Stick for GRUB
2 x HDD SAS 600GB 15K RPM - ZFS-Mirror-01 (ashift=9)
2 x HDD SAS 600GB 15K RPM - ZFS-Mirror-02 (ashift=9)

*Both Host and Guest VM are updated.

proxmox-ve: 6.3-1 (running kernel: 5.4.106-1-pve)
pve-manager: 6.3-6 (running version: 6.3-6/2184247e)
pve-kernel-5.4: 6.3-8
pve-kernel-helper: 6.3-8
pve-kernel-5.4.106-1-pve: 5.4.106-1
pve-kernel-5.4.73-1-pve: 5.4.73-1
ceph-fuse: 12.2.11+dfsg1-2.1+b1
corosync: 3.1.0-pve1
criu: 3.11-3
glusterfs-client: 5.5-3
ifupdown: 0.8.35+pve1
ksm-control-daemon: 1.3-1
libjs-extjs: 6.0.1-10
libknet1: 1.20-pve1
libproxmox-acme-perl: 1.0.8
libproxmox-backup-qemu0: 1.0.3-1
libpve-access-control: 6.1-3
libpve-apiclient-perl: 3.1-3
libpve-common-perl: 6.3-5
libpve-guest-common-perl: 3.1-5
libpve-http-server-perl: 3.1-1
libpve-storage-perl: 6.3-7
libqb0: 1.0.5-1
libspice-server1: 0.14.2-4~pve6+1
lvm2: 2.03.02-pve4
lxc-pve: 4.0.6-2
lxcfs: 4.0.6-pve1
novnc-pve: 1.1.0-1
proxmox-backup-client: 1.0.12-1
proxmox-mini-journalreader: 1.1-1
proxmox-widget-toolkit: 2.4-9
pve-cluster: 6.2-1
pve-container: 3.3-4
pve-docs: 6.3-1
pve-edk2-firmware: 2.20200531-1
pve-firewall: 4.1-3
pve-firmware: 3.2-2
pve-ha-manager: 3.1-1
pve-i18n: 2.3-1
pve-qemu-kvm: 5.2.0-5
pve-xtermjs: 4.7.0-3
qemu-server: 6.3-10
smartmontools: 7.2-pve2
spiceterm: 3.1-1
vncterm: 1.6-2
zfsutils-linux: 2.0.4-pve1
 
Last edited:
Hi,

## SATA

Run status group 0 (all jobs):
READ: bw=29.0MiB/s (30.4MB/s), 3339KiB/s-4435KiB/s (3419kB/s-4542kB/s), io=3692MiB (3871MB), run=124194-127245msec
WRITE: bw=30.2MiB/s (31.7MB/s), 3331KiB/s-4420KiB/s (3411kB/s-4526kB/s), io=3844MiB (4031MB), run=124194-127245msec


## IDE
Run status group 0 (all jobs):
READ: bw=30.2MiB/s (31.7MB/s), 3513KiB/s-4219KiB/s (3597kB/s-4320kB/s), io=3844MiB (4031MB), run=122728-127186msec
WRITE: bw=31.5MiB/s (33.1MB/s), 3947KiB/s-4377KiB/s (4041kB/s-4482kB/s), io=4012MiB (4207MB), run=122728-127186msec

As for another controller, what should I choose ?

1617381736457.png
 
Used 1M because I thought it should be easier to achieve better speeds then 4K blocks. When I am copying a big file over the LAN I get the speeds from the first test, 25-30MB/s. I even installed WS 2019 with latest virtio drivers and I get the same speeds.


fio --randrepeat=1 --ioengine=libaio --direct=0 --gtod_reduce=1 --name=test --filename=test --bs=4K --iodepth=32 --size=5G --readwrite=randrw --rwmixread=50 --numjobs=8 --time_based --runtime=120

## Host
Run status group 0 (all jobs):
READ: bw=3933KiB/s (4027kB/s), 481KiB/s-501KiB/s (492kB/s-513kB/s), io=461MiB (484MB), run=120018-120114msec
WRITE: bw=3929KiB/s (4023kB/s), 481KiB/s-497KiB/s (493kB/s-508kB/s), io=461MiB (483MB), run=120018-120114msec


## Guest VM
Run status group 0 (all jobs):
READ: bw=2347KiB/s (2403kB/s), 288KiB/s-296KiB/s (295kB/s-304kB/s), io=276MiB (289MB), run=120053-120305msec
WRITE: bw=2344KiB/s (2401kB/s), 285KiB/s-297KiB/s (292kB/s-304kB/s), io=275MiB (289MB), run=120053-120305msec


Like I said, I am new to Proxmox, maybe this speeds are ok ?
 
Before posting I tried with the default ashift=12 and the speed was lower with ~10MB/s with the same test and 1M block size.
 
I really wanted this to work but I am tired or testing and searching the internet for a fix.... back to Windows, Hyper-V and RAID...
 
proteus said:
I am new to Proxmox VE, I tried to find an answer for this problem with no luck.
The problem is that speed on Host is good but on Guest VM is very bad. I really tried all the cache types and 2 different ZFS Pools. The system specs are bellow for this test but i did tried on another Supermicro Server with AMD Epyc Rome and different HDD's with same results.


Test: Block 1M
fio --randrepeat=1 --ioengine=libaio --direct=0 --gtod_reduce=1 --name=test --filename=test --bs=1M --iodepth=32 --size=5G --readwrite=randrw --rwmixread=50 --numjobs=8 --time_based --runtime=120
Click to expand...

Hi @proteus

Your test is not OK, for several reasons:

- you test the host with fio for a dataset where cache is enable by default(so 1/2 RAM is usabable) and compare the result with VM test where the cache is only limited by the allocated RAM for that VM(give for your VM [1/2 of RAM - 1 GB] server and see the difference)
-the blocksize for a dataset is 128k compared with default VM who is 512 B, so oranges are not like apples
- even more the default Ubuntu install(and others) is done with LVM, so another layer with own block-size
- libaio option for fio is problematic for zfs, and your results will not be what you think you will see
- use end_fsync for fio, so you will be sure that all data test are write on the disk, and are not on the cache
proteus said:
When I am copying a big file over the LAN I get the speeds from the first test, 25-30MB/s. I even installed WS 2019 with latest virtio drivers and I get the same speeds.
Click to expand...

- I would also test the network speed, maybe is a problem here, maybe your switch use jumbo frames and your server is not using?

Good luck / Bafta
 
Hi, you are right, gave 10GB RAM to VM and same fio test with 1M block

Run status group 0 (all jobs):
READ: bw=55.1MiB/s (57.8MB/s), 6532KiB/s-7652KiB/s (6689kB/s-7835kB/s), io=6925MiB (7261MB), run=124110-125581msec
WRITE: bw=57.9MiB/s (60.7MB/s), 6648KiB/s-7717KiB/s (6807kB/s-7902kB/s), io=7267MiB (7620MB), run=124110-125581msec

Slightly better but this confirms that my tests are wrong and the memory cache is in my way.


Tried with this on the VM
fio --randrepeat=1 --ioengine=posixaio --direct=0 --gtod_reduce=1 --name=test --filename=test --bs=1M --iodepth=32 --size=5G --readwrite=randrw --rwmixread=50 --numjobs=8 --time_based --runtime=120 --end_fsync=1

Run status group 0 (all jobs):
READ: bw=35.4MiB/s (37.1MB/s), 4076KiB/s-4847KiB/s (4174kB/s-4964kB/s), io=7433MiB (7794MB), run=209755-209823msec
WRITE: bw=37.1MiB/s (38.9MB/s), 4437KiB/s-5140KiB/s (4544kB/s-5264kB/s), io=7783MiB (8161MB), run=209755-209823msec



The Network is fine, its copying with 1Gb/s until RAM is at 50% and then it goes down to 25-30MB/s
 
You must log in or register to reply here.
Top Bottom