Too slow windows startup on zfs?

O

ozgurerdogan

Renowned Member
May 2, 2010
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Bursa, Turkey, Turkey
Overall performance is good. But if I shutdown and start windows guest, startup is extremely slow.
I already set that is mentioned here
echo 1073741824 > /sys/module/zfs/parameters/zfs_arc_min
echo 4294967296 > /sys/module/zfs/parameters/zfs_arc_max

What could be problem? Server is 32 GB ram and have 5 vms each have 4 gb of ram. So Aroun 12 GB of ram is generally free.

I have 5 servers and all are same.
 
I saw a suggestion which was telling to set:
Code: 
echo never > /sys/kernel/mm/transparent_hugepage/enabled
echo never > /sys/kernel/mm/transparent_hugepage/defrag

Code: 
NAME        STATE     READ WRITE CKSUM
        rpool       ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            sda2    ONLINE       0     0     0
            sdb     ONLINE       0     0     0

Code: 
CPU BOGOMIPS:      49596.96
REGEX/SECOND:      1261878
HD SIZE:           1812.70 GB (rpool/ROOT/pve-1)
FSYNCS/SECOND:     15753.01
DNS EXT:           18.29 ms
DNS INT:           126.21 ms
 
What do you mean "using harddisks" ? The problem is only with windows guests. Not always but most of time, startup seems to me taking hours to complete. But after setting;
Code: 
echo never > /sys/kernel/mm/transparent_hugepage/enabled
echo never > /sys/kernel/mm/transparent_hugepage/defrag

seems normal now. Not sure if those setting would harm in future as one says "defrag".
 
Yes I usually set these:
Code: 
zfs set compression=on rpool
zfs set sync=disabled rpool
zfs set primarycache=all rpool
zfs set atime=off rpool
zfs set checksum=off rpool
zfs set dedup=off rpool
 
ozgurerdogan said:
Yes I usually set these:
Code: 
zfs set compression=on rpool
zfs set sync=disabled rpool
zfs set primarycache=all rpool
zfs set atime=off rpool
zfs set checksum=off rpool
zfs set dedup=off rpool
Click to expand...
This must by far be one of the worst advices ever given!
disable sync: Do not honour sync requests from applications and instead give applications the impression that data is safely persisted. I hope no database server is running on this disk
disable checksum: Effectively break ZFS' self healing feature which prevents bit rot etc. Also more or less makes scrubbing useless.
 
ozgurerdogan said:
My problem here is that windows gueest's startups' are too slow sometimes. I am really happy overall performance. And I am aware of those performance settings.
Click to expand...
I you consider your customers data of just modest value you would behave professionally and upgrade your hardware instead of gambling with the validity of there data!
 
mir said:
disable sync: Do not honour sync requests from applications and instead give applications the impression that data is safely persisted.
Click to expand...

{ This is not true. ZFS can not do sync writes. It only tell to the appl that ... yes, I do a sync}. In any case data on disk for zfs is ok with/without zfs sync on/off. But if you have some doubts about this, you can reduce the zfs flush time to disk from 5 seconds by default to 2-3 sec.
But I am agree with checksums=off it is a very bad ideea. This is the worst problem, and not the zfs sync on/off.

Late edit - I was wrong. I should say about faking O_DIRECT, and not about sync! My mistake, so thx. @mir
 
Last edited:
ozgurerdogan said:
My problem here is that windows gueest's startups' are too slow sometimes. I am really happy overall performance. And I am aware of those performance settings.
Click to expand...


same problem here. excellent performance, but if the vms is shut down and next started, the boot can take also 30 min (windows 2016/10)
 
Nemesiz said:
Build ZFS pool from 8 or more disk if you want fast VM startup, or use SSD only.
Click to expand...
i understand that a mirror of 2 drives is not the best setupm but i've shut down 1 vm (30 sec). Restarted and took exactly more than 30 min to boot a clean windows installation. I don't think this is normal.
 
It is normal. My ZFS pool with 2 hdd mirror or another pool with 3 hdd raidz VM startup takes some time. But in ZFS pool with 3 SSD raidz VM boots instantly.
 
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