Wondering about declining backup-speeds...

Discussion in 'Proxmox VE: Installation and configuration' started by Hans Otto Lunde, Mar 14, 2019.

  1. Hans Otto Lunde

    Hans Otto Lunde New Member

    Jul 13, 2017
    Likes Received:
    I feel that the speed of backup has declined lately, so I'm wondering, whar other people experience.
    My VM's run of a Synology NAS using NFS3 with a 10 gigabit/s link. The NAS itself has it's disks in a RAID6 configuration.
    If I test the disk-speed from within one of the Linux-VM's using 'dd' I get something like this for writing

    dd if=/dev/zero of=/data/test1.img bs=10G count=1 oflag=dsync
    0+1 records in
    0+1 records out
    2147479552 bytes (2.1 GB, 2.0 GiB) copied, 5.28242 s, 407 MB/s

    and for reads

    dd if=/data/test2.img of=/dev/zero bs=10G count=1 oflag=dsync
    0+1 records in
    0+1 records out
    2147479552 bytes (2.1 GB, 2.0 GiB) copied, 1.4855 s, 1.4 GB/s

    So reading is MUCH faster which is to be expected from a RAID6 system, I think. Anyway these are the numbers.
    When I backup I do it to another share on the same NAS, which will slow things down of course, I would guess about 50%. And then the lzo-compressor will have to do its work too, and there will be overhead etc, etc...
    But this is what I get at the moment using lzo-backup on a stopped VM:

    INFO: status: 8% (8638824448/10737410), sparse 2% (2342133760), duration 131, read/write 71/42 MB/s
    INFO: status: 9% (9709092864/10737410), sparse 2% (2735259648), duration 146, read/write 71/45 MB/s
    INFO: status: 78% (83767984128/10737410), sparse 47% (51305029632), duration 1123, read/write 74/0 MB/s
    INFO: status: 79% (84837662720/10737410), sparse 48% (52374708224), duration 1137, read/write 76/0 MB/s

    This is a Windows VM, that I'm backing up. I guess that the backup-system is not file-system aware, but simply backs up the whole diskspace of the VM sector-wise. Is this not the case? I think so, because my backups on windows-systems get quite a big smaller if I wipe the free-space on the VM's filesystem with 0's. You can also tell by the 0 MB/s writes in the second half of the backup-log-entries. Here it's backing up empty diskpace, which compresses to nearly nothing. Correct me if I'm completely wrong here.

    But anyway, is this the kind of speed I should expect backing up in this way? I seem to remember, that it used to be a lot faster, but I'm not absolutely sure. Has any of you experienced a slowdown of backups lately?

    Hans Otto Lunde
  2. czechsys

    czechsys Member

    Nov 18, 2015
    Likes Received:
    Your dd tests are useless. Use fio.
    And you forgot, backup is compressed. Thats a big slowdown.
    I never saw more than 200MBps for proxmox backup even against local ssd storage.
  3. mira

    mira Member
    Staff Member

    Feb 25, 2019
    Likes Received:
    We had some reports the last few weeks about backup speeds dropping but we still haven't identified the cause. Please post the output of 'pveversion -v' and the 'qm config' of all VMs affected.
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
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