Slow passthrough disk performance


New Member
Jun 1, 2023

I'm new on this forum, I write this post because I did not find an answer to this problem on the internet even ChatGPT failed to help me. I hope my English will be comprehensible :)

I have very poor performances (read/write) on my HDDs mounted (by passthrough) on my VM. About 3,4 MB/s read or write with `time dd if=/dev/zero of=/data/test.img bs=512M count=1`.
I do not have this issue with other partition. ( dd on / about 283 MB/s)

here is the configuration done on Proxmox:

qm set 103 -scsi1 /dev/disk/by-id/ata-XXX
qm set 103 -scsi2 /dev/disk/by-id/ata-XXX
qm set 103 -scsi3 /dev/disk/by-id/ata-XXX

here is the configuration done on the VM

parted /dev/sdc
(parted) mklabel gpt
(parted) unit TB
(parted) mkpart primary ext2 1M 100%
(parted) set 1 lvm on
parted /dev/sdd
parted /dev/sdb

pvcreate /dev/sdd1
pvcreate /dev/sdc1
pvcreate /dev/sdb1
vgcreate vg-raid /dev/sdd1 /dev/sdc1 /dev/sdb1

lvcreate -n lv-media --type raid5 -l 100%FREE vg-raid
mkfs.ext4 /dev/vg-raid/lv-media


/dev/mapper/vg--raid-lv--media /data ext4 defaults 0 0

I tried to change the Hard disk settings on Proxmox UI without success. Do you have any idea to help me see better performances?

thank you in advance :)
Bumping since I have a very similar situation. I have passed through a physical 8TB sata ssd to Ubuntu Server running Plex and Roon, I’m storing media files on the 8TB. When copying files to it I typically get a transfer speed of 56MB/s. The actual speed of the sata ssd is about 10x. Did I miss any essential setting? It’s passed through the same way as tonnulus.
What disk model do you got? As far as I understand there are 8TB SMR (shingled magnetic recording) HDDs these days and with SMR a HDD might just not be faster when writing.


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