Re: [gentoo-amd64] Is my RAID performance bad possibly due to starting sector value?

[Rich Freeman]

On Sat, Jun 22, 2013 at 8:49 AM, B Vance
<anonymous.pseudonym.88@×××××.com> wrote:
> Main advantage of using ZFS on linux is the ease of growing your pools.
> As long as you know the id of the drive (preferably the hardware id not
> the delegated one), its so simple I can manage it.  Since I'm nowhere
> near the technical level of most folk here, anyone can do it.  For what
> it's worth (very little I know), I think that ZFS has too many
> advantages over linux software RAID for it to be a real competition.

I'm holding out for btrfs but for all the same reasons.  I really
don't want to mess with zfs on linux (fuse, etc - and the license
issues - the thing I don't get is that Oracle maintains both).

However, the last time I checked ZFS does not support reshaping of
RAID-Z.  That is a major limitation for me, as I almost always expand
arrays gradually.  You can add additional raid-z's to a zpool, but if
you have a raid-z with 5 drives you can't add 1 more drive to it as
part of the same raid-z.  That means that it get treated as a mirror
and not a stripe, and that means that if you add 10 drives in this
manner one at a time you get 5 drives of capacity and not 9.  Btrfs
targets making raids re-shapeable, just like mdadm.

But in general COW makes a LOT more sense with RAID because the
layer-breaking allows them to often avoid read-write cycles by writing
complete stripes more often, and files aren't modified in place so you
can consolidate changes for many files into a single stripe (granted,
that can cause fragmentation).  ZFS has all those advantages being
COW, as will btrfs when it is ready for prime time.

Rich