Re: [PATCH 0/2 V2] btrfs: a new tool to manage a btrfs filesystem

[Chris Mason <chris.mason@oracle.com>]

On Thu, Feb 18, 2010 at 12:46:56PM -0800, Mike Fedyk wrote:
> On Thu, Feb 18, 2010 at 11:59 AM, Goffredo Baroncelli
> <kreijack@gmail.com> wrote:
> > On Thursday 18 February 2010, Chris Mason wrote:
> >> I do like the subcommand method, more details below.
> >>
> >
> > I try to summarise your suggestions. But there are some cases not t=
o clear for
> > me.
> > I grouped the commands in three categories: subvolume, devices, and
> > filesystem.
> >
> >
> > devices =A0 =A0 =A0 =A0 scan
> > devices =A0 =A0 =A0 =A0 show
> > devices =A0 =A0 =A0 =A0 balance
> > devices =A0 =A0 =A0 =A0 add
> > devices =A0 =A0 =A0 =A0 remove
> >
> > subvolume =A0 =A0 =A0 snapshot
> > subvolume =A0 =A0 =A0 delete
> > subvolume =A0 =A0 =A0 create
> > [subvolume =A0 =A0 =A0list]
> >
> > filesystem =A0 =A0 =A0resize
> > [filesystem =A0 =A0 label]
> >
> > ??? =A0 =A0 defrag
> > ??? =A0 =A0 sync
> >
> >
> >
> > For the first two categories both Chris and Mike agreed; but IMHO t=
here are
> > some commands that don't fit nor in devices, nor subvolume, like re=
size (we
> > resize a filesystem) and label (not available now).
> >
>=20
> A btrfs filesystem can span multiple devices.  Resize resizes how big
> of a chunk of one device btrfs uses.

Right, resize is actually always per device.  When there is one device
resizing the FS and the device are the same thing.

> This would be used by
> partitioning programs for instance.  zfs uses the term "pool" instead
> of filesystem to solve this ambiguous use of the term "filesystem"
> since btrfs and zfs break people's existing definition of the word
> "filesystem".
>=20
> > I don't know how classify defrag (per file / directory level ?) and=
 sync
> > (filesystem ?)
>=20
> It turns out that defrag is per file, which seems most cumbersome.
> Maybe since it will probably eventually work against several types of
> objects we could have:
>=20
> btrfs defrag file <file>
> btrfs defrag directory <directory>
> btrfs defrag subvol <subvol>

I like these, although we don't currently support the directory/subvol
side.  But we can leave the option open to add these later.

> btrfs defrag pool <pool>

I don't think we'll need defrag pool.

>=20
> >
> > An option is to consider commands without classification. For examp=
les:
> >
> > $ btrfs subvolume create [path/]<subvolname>
> > $ btrfs sync <path>
> > $ btrfs defrag <file>
>=20
> Maybe if the btrfs developers are agreeable, we could do this as well=
:
>=20
> btrfs sync file <file>
> btrfs sync directory <directory>

fsync on files and dirs already does this, we don't need a btrfsctl for
it.

> btrfs sync subvol <subvol>

btrfs sync subvol is nice.

> btrfs sync pool <pool>
>=20

I don't think we need sync pool.

-chris

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