Date: Thu, 22 Jul 2010 19:50:18 +0930 From: "Daniel O'Connor" <doconnor@gsoft.com.au> To: Dan Langille <dan@langille.org> Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: Using GTP and glabel for ZFS arrays Message-ID: <3D5AABDD-F51B-4B7A-BC7F-BAA72F829A21@gsoft.com.au> In-Reply-To: <4C47B57F.5020309@langille.org> References: <4C47B57F.5020309@langille.org>
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On 22/07/2010, at 12:35, Dan Langille wrote:
> Why use glabel?
>=20
> * So ZFS can find and use the correct HDD should the HDD device ever
> get renumbered for whatever reason. e.g. /dev/da0 becomes /dev/da6
> when you move it to another controller.
>=20
> Why use partitions?
>=20
> * Primarily: two HDD of a given size, say 2TB, do not always provide
> the same amount of available space. If you use a slightly smaller
> partition instead of the entire physical HDD, you're much more
> likely to have a happier experience when it comes time to replace an
> HDD.
>=20
> * There seems to be a consensus amongst some that leaving the start =
and
> and of your HDD empty. Give the rest to ZFS.
I would combine both!
GPT generates a UUID for each partition and glabel presents this so ZFS =
can use it, eg I have..
[cain 19:45] ~ >sudo zpool status
pool: tank
state: ONLINE
scrub: none requested
config:
NAME STATE READ =
WRITE CKSUM
tank ONLINE 0 =
0 0
raidz2 ONLINE 0 =
0 0
gptid/d7467802-418f-11df-bcfc-001517e077fb ONLINE 0 =
0 0
gptid/d7eeeced-418f-11df-bcfc-001517e077fb ONLINE 0 =
0 0
gptid/d8761aa0-418f-11df-bcfc-001517e077fb ONLINE 0 =
0 0
gptid/d9083d18-418f-11df-bcfc-001517e077fb ONLINE 0 =
0 0
gptid/d97203ec-418f-11df-bcfc-001517e077fb ONLINE 0 =
0 0
and on each disk..
[cain 19:46] ~ >gpart list ada0 =20
Geom name: ada0
fwheads: 16
fwsectors: 63
last: 1953525134
first: 34
entries: 128
scheme: GPT
Providers:
1. Name: ada0p1
Mediasize: 8589934592 (8.0G)
Sectorsize: 512
Mode: r0w0e0
rawtype: 516e7cb5-6ecf-11d6-8ff8-00022d09712b
label: (null)
length: 8589934592
offset: 17408
type: freebsd-swap
index: 1
end: 16777249
start: 34
2. Name: ada0p2
Mediasize: 991614917120 (924G)
Sectorsize: 512
Mode: r1w1e2
rawtype: 516e7cba-6ecf-11d6-8ff8-00022d09712b
label: (null)
length: 991614917120
offset: 8589952000
type: freebsd-zfs
index: 2
end: 1953525134
start: 16777250
Consumers:
1. Name: ada0
Mediasize: 1000204886016 (932G)
Sectorsize: 512
Mode: r1w1e3
The only tedious part is working out which drive has what UUIDs on it =
because gpart doesn't list them.
The advantage of using the UUIDs is that if you setup another machine =
the same way you don't have to worry about things when you plug in the =
disks from it to recover something. Or perhaps you are upgrading at the =
same time as replacing hardware so you have all the disks in at once.
> Create a new partition within that scheme:
>=20
> gpart add -b 34 -s SOMEVALUE -t freebsd-zfs ad0
>=20
> Why '-b 34'? Randi pointed me to =
http://en.wikipedia.org/wiki/GUID_Partition_Table where it explains what =
the first 33 LBA are used for. It's not for us to use here.
If you don't specify -b it will DTRT - that's how I did it.
You can also specify the size (and start) in human units (Gb etc).
--
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum
GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C
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