[PVE-User] Proxmox + ZFS: Performance issues

[Adam Thompson]

Perhaps irrelevant,  but a colleague of mine recently solved a puzzling performance issue merely by replacing the existing SATA cables with new, properly-rated cables.
Turns out, much like USB v1 vs USB v2, there's next to nothing distinguishing SATA I cables vs SATA II cables vs SATA III cables, except for unusually poor performance when used at too high a speed.
Only the magnitude of your performance drop suggests this; also the fact that you get good raw read performance, which mirrors the symptoms in the SATA cable case precisely.
-Adam

On April 24, 2016 11:49:38 AM CDT, Robert Fantini <robertfantini at gmail.com> wrote:
>if those are not ssd drives, then  adding a zil drive will most likely
>help.
>
>On Sat, Apr 23, 2016 at 2:15 PM, Ralf <ralf+pve at ramses-pyramidenbau.de>
>wrote:
>
>> Hi,
>>
>> I encounter very bad read/write performance on my mirror-zfs, even on
>> hypervisor-side.
>>
>> After shutting down all VMs, reading and writing from raw ZFS block
>> devices VMs runs at maximum 5MiB/s (tested with dd
>> if=/dev/rpool/VM/disk-100 of=/dev/null) while reading from the
>> underlying raw-disk (/dev/sda) has good performance (~100MiB/s). Of
>> course, performance inside VMs is even worse. Any ideas?
>>
>> This is my setup:
>> Proxmox / 4.1-30/9e199213 / Linux 4.4.6-1-pve / ZFS mirror, two disks
>>
>> ZFS setup:
>>
>> $ dmesg | grep ZFS
>> [    2.882118] ZFS: Loaded module v0.6.5.6-1, ZFS pool version 5000,
>ZFS
>> filesystem version 5
>>
>> $ zpool status
>>         [snip]
>>         NAME        STATE     READ WRITE CKSUM
>>         rpool       ONLINE       0     0     0
>>           mirror-0  ONLINE       0     0     0
>>             sdb2    ONLINE       0     0     0
>>             sda2    ONLINE       0     0     0
>>
>> ZFS module parameters:
>> $ cat /etc/modprobe/zfs.conf
>> options zfs zfs_arc_max=3221225472
>>
>> Partition alignement:
>> $ parted /dev/sda
>> (parted) align-check o 2
>> 2 aligned
>>
>> Dedup: off
>> Checksumming: on
>> Compression: off
>>
>> Anything helps!
>>
>> Cheers
>>   Ralf
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>>
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