Am Sonntag, 11. September 2016, 18:27:30 CEST schrieben Sie:
> What is the smallest recommended fs size for btrfs?
>
> - There are mentions of 256MB around the net.
> - Gparted reserves minimum of 256MB for btrfs.
>
> With an ordinary partition on a single disk,
> fs created with just "mkfs.btrfs /dev/sdxx":
> - 128MB works fine.
> - 127MB works but as if it is 64MB.
>
> Can we say size should be in multiples of 64MB?
Do you want to know the smalled *recommended* or the smallest *possible* size?
I personally wouldn´t go below one or two GiB or or so with BTRFS. On small
filesystems, I don´t know the treshold right now it uses a mixed metadata/data
format. And I think using smaller BTRFS filesystem invited any left over
"filesystem is full while it isn´t" issues.
Well there we go. Excerpt from mkfs.btrfs(8) manpage:
-M|--mixed
Normally the data and metadata block groups are isolated.
The mixed mode will remove the isolation and store both
types in the same block group type. This helps to utilize
the free space regardless of the purpose and is suitable
for small devices. The separate allocation of block groups
leads to a situation where the space is reserved for the
other block group type, is not available for allocation and
can lead to ENOSPC state.
The recommended size for the mixed mode is for filesystems
less than 1GiB. The soft recommendation is to use it for
filesystems smaller than 5GiB. The mixed mode may lead to
degraded performance on larger filesystems, but is
otherwise usable, even on multiple devices.
The nodesize and sectorsize must be equal, and the block
group types must match.
Note
versions up to 4.2.x forced the mixed mode for devices
smaller than 1GiB. This has been removed in 4.3+ as it
caused some usability issues.
Thanks
--
Martin
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