Date: Sun, 09 Jan 2011 10:49:59 +0000 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Jean-Yves Avenard <jyavenard@gmail.com> Cc: freebsd-stable@freebsd.org Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks Message-ID: <4D2992D7.9090009@infracaninophile.co.uk> In-Reply-To: <AANLkTikEz-WgPX53WmOe4wCmXid_u59bTX0EdjqrkFQz@mail.gmail.com> References: <4D1C6F90.3080206@my.gd> <ifsia5$5ub$2@dough.gmane.org> <4D21E679.80002@my.gd> <84882169-0461-480F-8B4C-58E794BCC8E6@my.gd> <BEBC15BA440AB24484C067A3A9D38D7E0149F32D13E3@server7.acsi.ca> <m262ty39th.wl%randy@psg.com> <4D297587.4030108@infracaninophile.co.uk> <AANLkTikn2G_23M3PbERTo8KR3sDqxkhWr=OntA4cVwh9@mail.gmail.com> <4D2987E0.7060701@infracaninophile.co.uk> <AANLkTikEz-WgPX53WmOe4wCmXid_u59bTX0EdjqrkFQz@mail.gmail.com>
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On 09/01/2011 10:24, Jean-Yves Avenard wrote:
> On 9 January 2011 21:03, Matthew Seaman <m.seaman@infracaninophile.co.u=
k> wrote:
>=20
>>
>> So you sacrifice performance 100% of the time based on the very unlike=
ly
>> possibility of drives 1+2 or 3+4 failing simultaneously, compared to t=
he
>> similarly unlikely possibility of drives 1+3 or 1+4 or 2+3 or 2+4
>=20
> But this is not what you first wrote
What I said was:
> >> Note: raidz2 on 4 disks doesn't really win you anything over 2 x mir=
ror
> >> pairs of disks, and the RAID10 mirror is going to be rather more
performant.
> You said the effect were identical. they are not.
Which is certainly not saying the effects are identical. It's saying
the difference is too small to worry about.
> Plus, honestly, the difference in performance between raidz and raid10
> is also close to bein insignificant.
That's not my experience. It depends on what sort of workload you have.
If you're streaming very large files, I'd expect RAID10 and RAIDz to be
about equal. If you're doing lots of randomly distributed small IOs,
then RAID10 is going to win hands down.
Cheers
Matthew
--=20
Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
JID: matthew@infracaninophile.co.uk Kent, CT11 9PW
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