Use whole disk

Use whole disk

[Ramon Hofer]

Hi all

I hope this is the right place to ask this:

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:

~# mkfs.xfs /dev/sdk

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?


Best regards
Ramon

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Re: Use whole disk

[Ramon Hofer]

On Tue, 03 Jul 2012 07:50:49 +0000, Ramon Hofer wrote:

> Is it ok to use the disk instead of the partition or why do I have to
> create the filesystem on a partition?

I was told that it's possible to use the whole disk. But it's safer 
because the user (me) and some tools see that the disk is already used 
because of the valid partition table.

Another reason would be the filesystem alignment that could cause 
performance issues.


Best regards
Ramon

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Re: Use whole disk

[Stan Hoeppner]

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. ;)

> 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?

> ~# mkfs.xfs /dev/sdk

If yes, did mkfs.xfs throw a warning about overwriting the partition table?

> 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.

-- 
Stan

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Re: Use whole disk

[Ramon Hofer]

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 :-)


Cheers
Ramon

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