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Date:      Tue, 09 Dec 2008 10:58:25 +0100
From:      Ivan Voras <ivoras@freebsd.org>
To:        freebsd-fs@freebsd.org
Subject:   Re: ZFS resize disk vdev
Message-ID:  <ghlfg0$lpd$1@ger.gmane.org>
In-Reply-To: <493E12EC.4050801@modulus.org>
References:  <92f477740812082155y3365bec7v5574206dd1a98e26@mail.gmail.com> <493E12EC.4050801@modulus.org>

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Andrew Snow wrote:
> Bryan Alves wrote:
>> I'm thinking about using a hardware raid array with ZFS, using a
>> single disk
>> vdev zpool.  I want the ability to add/remove disks to an array, and I=
'm
>> still unsure of the stability of zfs as a whole.  I'm looking for an e=
asy
>> way to resize and manage disks that are greater than 2 terabytes.
>> If I have a single block device, /dev/da0, on my system that is
>> represented
>> by a zfs disk vdev, and the size of this block device grows (because t=
he
>> underlying hardware raid expands), will zfs correctly expand?  And
>> will it
>> correctly expand in place?
>=20
> In theory, this works fine - I have never tried it myself.  The only
> other way to expand a zpool is by adding more vdevs:  You cannot change=

> a vdev once it is created other than to take it from a single disk to a=

> mirror.
>=20
> Sun's ZFS best practice guide states that you should avoid a single dis=
k
> vdev  because performance on the whole suffers and is worse than UFS.
>=20
> I am going to publish some benchmark figures soon to back this up, base=
d
> on testing I did with a 16 disk hardware RAID6.  ZFS was *alot* faster
> when I gave it the disks in a RAIDZ2 vdev.

You mean it was a lot faster *per disk*, right? (otherwise, it's
completely expected that a large RAID array will be faster than its
components).


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