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Date:      Sun, 15 Nov 2009 01:19:29 -0000
From:      "Graeme Dargie" <arab@tangerine-army.co.uk>
To:        "FreeBSD Questions" <freebsd-questions@freebsd.org>
Subject:   RE: ZFS disk replacement questions
Message-ID:  <01FB8F39BAD0BD49A6D0DA8F7897392904F747@Mercury.galaxy.lan.lcl>
In-Reply-To: <d36406630911040119v6254d21ehbf3963b90eb1e84b@mail.gmail.com>
References:  <d5eb95fc0911030937n15bc2c9h73866ca6c7788216@mail.gmail.com><4AF07493.7050208@comcast.net><d5eb95fc0911031132g264182c9qf1c4d51bb1ea2086@mail.gmail.com><4AF08A42.9000900@comcast.net> <d36406630911040119v6254d21ehbf3963b90eb1e84b@mail.gmail.com>

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-----Original Message-----
From: krad [mailto:kraduk@googlemail.com]=20
Sent: 04 November 2009 09:19
To: Steve Polyack
Cc: Derrick Ryalls; FreeBSD Questions
Subject: Re: ZFS disk replacement questions

2009/11/3 Steve Polyack <korvus@comcast.net>

> Derrick Ryalls wrote:
>
>> On Tue, Nov 3, 2009 at 10:21 AM, Steve Polyack <korvus@comcast.net>
>> wrote:
>>
>>
>>> 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
>>> disks.
>>>  This way you can name them in a way that makes sense to you.
>>>  Additionally,
>>> 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
>>> devices
>>> to be numbered differently (i.e. a drive dies and you happen to
reboot
>>> the
>>> system).
>>>
>>>
>>
>> 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
>> drive.
>>
>>
>>
> 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
>>> the
>>> 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
the benefits
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Hi All

Sorry to jump in on someone else's question / answer but I have a
related query. I notice the previous answer mentioned specific achi(4)
driver and Freebsd 8.0 are these available in 7.2 ? Will the achi(4)
driver work happily along side the ata driver. I just replaced every
drive in my raidz array the dirty way as I could not see away to make
the replacement drive show up without doing a reboot, would the achi(4)
driver allow me to hot swap the disks in the future ?

Regards

Graeme




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