Re: Speed up mount time?

[Forza <forza@tnonline.net>]

---- From: Joakim <ahoj79@gmail.com> -- Sent: 2022-11-23 - 13:33 ----

> I have a couple of machines (A and B) set up where each machine has a
> ~430 TB BTRFS subvolume, same data on both. Mounting these volumes
> with the following flags: noatime,compress=lzo,space_cache=v2
> 
> Initially mount times were quite long, about 10 minutes. But after i
> did run a defrag with -c option on machine B the mount time increased
> to over 30 minutes. This volume has a little over 100 TB stored.
> 
> How come the mount time increased by this?

You now have now extents to keep track of, which means more metadata to parse at mount. 

> 
> And is there any way to decrease the mount times? 10 minutes is long
> but acceptable, while 30 minutes is way too long.
> 
> Advice would be highly appreciated. :)
> 

You can defrag the subvolume and extent trees by using `btrfs fi defrag /path/to/subvol`. You can do this on each subvol and on the top level volume. This can reduce amounts of seeks, improving performance some. 

> 
> 
> Linux sm07b 5.4.17-2136.311.6.1.el8uek.x86_64 #2 SMP Thu Sep 22
> 19:29:28 PDT 2022 x86_64 x86_64 x86_64 GNU/Linux
> btrfs-progs v5.15.1
> Label: 'Storage'  uuid: 6ecd172e-3ebd-478c-9515-68162a41590d
>         Total devices 1 FS bytes used 105.04TiB
>         devid    1 size 436.57TiB used 107.87TiB path /dev/sdb
> 
> Data, single: total=107.34TiB, used=104.82TiB
> System, DUP: total=40.00MiB, used=11.23MiB
> Metadata, DUP: total=269.00GiB, used=221.57GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
> 
> [   51.764445] BTRFS info (device sdb): flagging fs with big metadata feature
> [   51.764450] BTRFS info (device sdb): use lzo compression, level 0
> [   51.764454] BTRFS info (device sdb): using free space tree
> [   51.764455] BTRFS info (device sdb): has skinny extents