[linux-lvm] Unusually long boot times with LVM Snapshots
sreyan32 at gmail.com
Fri Nov 20 16:18:10 UTC 2020
On Fri, Nov 20, 2020 at 4:45 PM Bryn M. Reeves <bmr at redhat.com> wrote:
> What type of snapshot are you using? LVM2 allows either "classic" CoW
> or the newer thin provisioned snapshots using the dm-thinp target.
> Classic snapshots are known to have very poor IO performance when multiple
> snapshots of the same volume exist simultaneously (especially for write-
> heavy workloads).
> Thin provisioned snapshots are not normally activated at boot time unless
> they are explicitly requested (via dracut's rd.lvm.lv options) since they
> have the skip activation flag set by default.
How can I check which type of snapshot I am using ?
I am very interested in knowing more about these newer snapshots.
I think I am using the older COW snapshots.
I created it using:
sudo lvcreate -L 70GB -s -n test_snapshot
Is there any indication in the log of what's happening during the delay?
> Look through the journalctl output to see if there are any messages logged
> while the delay happens.
Yes, I have found the reason for the 3 minute delay:
Nov 20 21:14:15 dracut-initqueue: Scanning devices dm-0 for LVM
logical volumes vgfedora/fedora
Nov 20 21:14:16 dracut-initqueue: inactive Original
'/dev/vgfedora/fedora' [700.00 GiB] inherit
Nov 20 21:14:16 dracut-initqueue: inactive Snapshot
'/dev/vgfedora/pre_kde_Nov_9' [70.00 GiB] inherit
Nov 20 21:17:27 systemd: Found device /dev/mapper/vgfedora-fedora.
Nov 20 21:17:27 systemd: Found device
Nov 20 21:17:27 systemd: Reached target Initrd Root Device.
As you can see it initializing the snapshots.
This is my entire boot log if you need to delve deeper.
> Another option is to use systemd-analyze to look into where the time is
> going during boot. It has various commands including "plot" which will
> generate an SVG plot of the boot timings on stdout. You can then compare
> that with a regular boot to try to understand the difference.
Well I don't know about "plot" but this is the output from "systemd-analyze
3min 30.737s dracut-initqueue.service
17.725s systemd-cryptsetup at luks\x2d2ec7f1ae\x2d6f9b\x2d4896\x2da7b2\x2dbe7809e9d2f4.service
As you can see the 3min delay matches with the above LVM entry from the
Again, I am very interested in knowing more about these newer snapshots.
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