On Thu, May 24, 2018 at 03:38:15PM +1000, Paul van den Bergen wrote:
> I currently take the approach that unless I have specific IO needs for a
> volume, I will work with one partition for OS and data as it is the most
> efficient use of disk space.

This is true for standard partitioning, or LVM logical volumes.  It's not
true for either btrfs or zfs.  Disk usage efficiency for them is completely
unaffected by using multiple sub-volumes/datasets.

With partitions or LVs you have to decide how big you want them at the time
you create them.  Changing their size is a moderately complicated task - not
terribly difficult once you know how to do it, but it does require care and
attention to detail to ensure you don't screw it up. and depending on the
filesystem the partition or LV is formatted with, you may be restricted to
only growing the partition, never shrinking it (which makes, e.g., shrinking
/home to grow / even more of a PITA)

With sub-volumes on btrfs and datasets on zfs, they just share space on the
entire pool. Unless you set entirely optional quotas or reservations, you will
never have to resize anything.  And if you do set a quota or reservation,
it's trivially easy and risk-free to change them at any time...they're "soft"
limits, not hard.

I used to do one big partition for everything - same as you, for the same
reason.  Now I use zfs datasets so that I can enable different attributes
(like compression type, acl types, quotas, recordsize, etc) for specific
needs - e.g. mysql and postgres perform better if their files are stored on a
dataset where the recordsize is 8K rather than the ZFS default of 128K. And
systemd's journald complains if it can't use posix acls, so I'm getting into
the habit of setting 'acltype=posixacl' and 'xattr=sa' on /var/log for my zfs
machines.  And using gzip rather than lz4 for /var/log too.  Videos, music,
and deb files are already compressed so their datasets have 'compression=off'.


Having /home and /var and other directories separated from / is useful - but
in the old days of fixed partition sizes, it just wasn't worth the hassle
or the risk of running out of space on one partition while there's plenty
available on other partitions. Now it's no hassle or risk at all.

> synology takes the first slice (~2-3GB) of every disk in the device and
> makes a RAID 1 volume for the operating system, then does the same with the
> second slice to make a swap partition.  You can lose all but one disk and
> still have a bootable working machine.  the rest of the disk is available
> to make volumes out of.

yep, this is a good idea.  it's similar to what I do on all my machines.


craig

--
craig sanders <cas@taz.net.au>

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