ZFS disk replacement questions
kraduk at googlemail.com
Wed Nov 4 09:19:15 UTC 2009
2009/11/3 Steve Polyack <korvus at comcast.net>
> Derrick Ryalls wrote:
>> On Tue, Nov 3, 2009 at 10:21 AM, Steve Polyack <korvus at comcast.net>
>>> Derrick Ryalls wrote:
>>>> 1) In the event of a disk failure, how do I trace back the name such
>>>> as adX to a physical drive in the enclosure? Is there a way to take
>>>> the drive offline then use atacontrol to spin it down or something so
>>>> it is easy to identify?
>>> In my opinion you are best off using glabel(8) to give names to the
>>> This way you can name them in a way that makes sense to you.
>>> when you create the ZFS pool you will use the glabel'd names. This means
>>> that the pool will still come up properly if something causes your
>>> to be numbered differently (i.e. a drive dies and you happen to reboot
>> I believe ZFS does this automatically. Supposedly, if you take a
>> working set of RAIDZ drives from one machine and put it in another,
>> ZFS will figure out the drives since they get labelled by ZFS
>> internally. My question concerns how to identify the physical disk in
>> question based on the adX or glabel name? Different name in software
>> is fine, but if the drive fails I want to make sure I pull the correct
> This is possible, but I don't remember reading that ZFS handles this
> anywhere, and I've seen glabel(8) recommended elsewhere for the same reason.
> Either way, you can add your drives one-by-one and label them on the
> enclosure "arraydrive00" and then glabel the individual disks with the same
> name. This way when ZFS tells you "arraydrive03" is dead/offline, you can
> look at your enclosure and pull the drive with the arraydrive03 label.
> Depending on your controller it is also probably worth it to use one of
>>> SATA-specific drivers in FreeBSD 8 - these are ones like ahci(4) and
>>> siis(4). While the generic ata(4) driver will work for pretty much
>>> everything, the updated AHCI drivers can take advantage of some more
>>> features. Enable the modules at boot to use them.
>> I will look into it, thanks. The machine in question is 2 year old
>> hardware currently with a 3ware raid card. I will be going software
>> raid only, but FreeBSD already recognizes the eSATA drive I have
>> attached as a backup device so I know the O/S can at least talk to
>> sata drives attached to the mobo.
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One thing to note about resilvering; unlike most raid systems zfs knows what
is going on at the filesystem level as well as block level. Therefore when a
drive has to be resilvered, only the data on the drive is rebuilt rather
than every block as with most other raid subsystems. eg if you have a 1TB hd
but only have 20 Gig of data, only 20 gig is copied/rebuilt rather than 1 TB
of data if you were using gvinum/gmirror. This massively speeds up rebuild
times and stress on the other drives. However the fuller the drive the less
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