zfs initializes slowly on hardware, fast on VM

[twork]

System information

Type	Version/Name
Distribution Name: Ubuntu
Distribution Version: 19.04
Linux Kernel: #17-Ubuntu SMP Wed May 15 10:52:21 UTC 2019
Architecture: x86_64
ZFS Version: 0.7.12-1ubuntu5
SPL Version: 0.7.12-1ubuntu3

Describe the problem you're observing

I've built two fresh installs with zfs on the base filesystem. On the VM, it runs fine. But on the hardware instance, while it runs normally after it's through booting, the filesystems initialize so slowly I thought the OS had hung.

Describe how to reproduce the problem

I'm following the "ZFS on Ubuntu" guide, at:

https://github.com/zfsonlinux/zfs/wiki/Ubuntu-18.04-Root-on-ZFS

The only thing unusual that I find is (on both) the system is run on three disks instead of just one, so instead of:

zpool create -f -o ashift=12 [...settings copied from the HOWTO...] -R /mnt bpool [disk]

...I have, on both VM and hardware:

zpool create -f -o ashift=12 [...settings copied from the HOWTWO...] -R /mnt bpool raidz [three disks]

Since I'm using Ubuntu 19.04, there are a few differences, mostly minor; overall it seems to go just fine. My test instance, a VM on VirtualBox, has run with no issues.

Trouble appears on hardware, an old-ish PC. Initial setup runs fine, no problems appearing. But when I boot the host after installing it, it runs fine until we reach the initial mount of the boot filesystem, and then again when the root tries to mount. Those each pause for several minutes, so long that at first I'd thought that the OS had hung when it initializes.

I've been looking for other instances of this problem and haven't been able to find any. Maybe I'm just not putting the right words into Google, so hints are welcome.

The closest I've been able to come is a case where someone was having trouble that was similar and on the same Ubuntu release as me, though the pauses were not as extreme -- maybe 20-30 seconds rather than several minutes. There, it was fixed by replacing 'zfs-initramfs' with 'zfs-dracut', so I tried it here, but that made no difference in this case. VM is still fine, hardware still pauses for several minutes at two stages of the boot process.

Include any warning/errors/backtraces from the system logs

[qt-br]

Might be related to the fact that VirtualBox by default doesn't flush data immediately to disk, see:
https://www.virtualbox.org/ticket/7143

"If desired, the virtual disk images can be flushed when the guest issues the IDE FLUSH CACHE command. Normally these requests are ignored for improved performance."
https://www.virtualbox.org/manual/ch12.html#idm10187

[twork]

Thanks, all. A brief update here: As it happens, my most recent boot on this machine was with with zfs-initramfs installed; to answer about rd.debug, I have to switch back to zfs-dracut, and apparently I overlooked something when I apt install'ed back to that, because now the boot throws up an emergency shell. That hasn't happened before... Obviously, each time I reboot it's a long wait; I've done this before, expect to have it right the next time, but since boots are so slow this is going to take a while. Bear with me. Meanwhile: looking at: https://www.virtualbox.org/ticket/7143 ...I don't catch what I should be understanding here. Hint? Thanks.

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On Wed, Jun 19, 2019 at 5:35 AM Grupo Brasileiro de Qt < ***@***.***> wrote: Might be related to the fact that VirtualBox by default doesn't flush data immediately to disk, see: https://www.virtualbox.org/ticket/7143 — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#8928>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AASWMK2ACWADHOH3AALLY5TP3IDWFANCNFSM4HZDRQUQ> .

[twork]

kpande said:

can you provide output from rd.debug cmdline option with zfs-dracut?

On the (hardware) system I've been restarting from scratch. I'm up to the point where I'd answer this question, and now I realize I don't follow it. Where would I find the answer to this?

Maybe relevant: in the HOWTO that I'm working from (referenced above), one step is to run:

update-initramfs -u -k all

...after grub-probe and before update-grub. And, that command doesn't exist since I rebuilt the machine with dracut/zfs-dracut instead of initramfs. I haven't looked yet but I'm guessing that I should be running a different command to replace that. Hints welcome; I'll go looking.

[stale]

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