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Re: Use whole disk

To: stan@xxxxxxxxxxxxxxxxx
Subject: Re: Use whole disk
From: Ramon Hofer <ramonhofer@xxxxxxxxxx>
Date: Tue, 03 Jul 2012 11:10:31 +0200
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <4FF2B183.1050304@xxxxxxxxxxxxxxxxx>
References: <jsu88p$t01$1@xxxxxxxxxxxxxxx> <4FF2B183.1050304@xxxxxxxxxxxxxxxxx>
On Die, 2012-07-03 at 03:46 -0500, Stan Hoeppner wrote:
> On 7/3/2012 2:50 AM, Ramon Hofer wrote:
> > Hi all
> Hi Ramon, welcome to XFS.
> > I hope this is the right place to ask this:
> It is.  But I could have answered this, and any of your XFS questions,
> off list as well. ;)

Yes, I know.
But I didn't want to abuse you as my personal question answering
machine ;-)

> > I wanted to use a 2 TB disk (as mythtv recordings drive) with the xfs 
> > filesystem. Until now I had jfs but I wanted to switch it.
> > 
> > Since I have two drives of the same type I formatted the new drive with 
> > xfs and copied the recordings onto it. Today I saw that I created the 
> > filesystem over the disk instead of the partition:
> Had you already put a partition on the disk?

Yes, I have.

> > ~# mkfs.xfs /dev/sdk
> If yes, did mkfs.xfs throw a warning about overwriting the partition table?

Yes, it did. And I was confused because I thought the warning was
because the disk was in the md9 raid before. But since I have
overwritten the raid partition now I realize that the warning was about
the partition I created afterwards...

> > These are my two disks:
> > 
> > /dev/sdi1      jfs    1.9T  1.9T  3.9G 100% /mnt/recordings
> > /dev/sdk       xfs    1.9T  1.9T  3.3G 100% /mnt/recordings_temp
> > 
> > Is it ok to use the disk instead of the partition or why do I have to 
> > create the filesystem on a partition?
> It's not necessary to put a partition on the disk before formatting with
> XFS.  And in fact, when using Advanced Format drives, it's much easier
> to make sure XFS is sector aligned by directly formatting the disk.
> Partitioning an AF drive to get proper sector alignment can be tricky.
> If you don't get proper sector alignment of the partition, you end up
> with a read/modify/write cycle when a filesystem block is modified.
> This reduces the performance of the drive significantly.  For a write
> mostly mythTV recording drive this probably isn't critical.  But if you
> can avoid the misaligned sector problem it's best to do so.  And you
> easily can by directly formatting the disk device.

So it's better to directly format the disk and not the partition.

I will redo that :-)


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