[linux-lvm] Partitions on same Drive

[linux-lvm] Partitions on same Drive

[Rene Schumann]

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Hello!

I have a Problem and hope someone here can help me.
I have 2 Partitions on a drive.

[root@desktop root]# fdisk -l /dev/sdb

Festplatte /dev/sdb: 255 Köpfe, 63 Sektoren, 9730 Zylinder
Einheiten: Zylinder mit 16065 * 512 Bytes

    Gerät Booten  Anfang      Ende   Blöcke   ID  Dateisystemtyp
/dev/sdb1             1      4462  35840983+   c  Win95 FAT32 (LBA)
/dev/sdb2          4463      9730  42315210   8e  Linux LVM

I want to delete sdb1 vfat partition and use it as LVM space.
If i do a "pvcreate vg01 /dev/sdb1" it is ugly for performance because
there are 2 LVM Partions at one drive.
right?
If i do lvm partition on sdb1 and do a pvmove,
Can i resize sdb1 to fit the whole drive and after that lvm use this
full space? 

thx you
mfg
Rene

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Re: [linux-lvm] Partitions on same Drive

[Luca Berra]

On Mon, Jan 21, 2002 at 09:42:37PM +0100, Rene Schumann wrote:
>    /dev/sdb1             1      4462  35840983+   c  Win95 FAT32 (LBA)
>    /dev/sdb2          4463      9730  42315210   8e  Linux LVM
>    I want to delete sdb1 vfat partition and use it as LVM space.
>    If i do a "pvcreate vg01 /dev/sdb1" it is ugly for performance because
>    there are 2 LVM Partions at one drive.
>    right?
>    If i do lvm partition on sdb1 and do a pvmove,
>    Can i resize sdb1 to fit the whole drive and after that lvm use this
>    full space?
you cannot resize a PV.
if you don't create striped LVs on the two partitions i see no
significant performance problem.

L.


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Re: [linux-lvm] Partitions on same Drive

[mitch]

> if you don't create striped LVs on the two partitions i see no
> significant performance problem.

Brings up a question ... can you get improved performance by striping to
multiple devices on the same SCSI channel, or do they really need to be on
separate SCSI channels for good performance?  Ex: I have a fibre channel
card, and multiple drives I'm gonna hook up ... someday.  Can I strip
across all the drives and expect to push fibre channel's capabilities?

-- Mitch

Re: [linux-lvm] Partitions on same Drive

[James Hawtin]

On 21 Jan 2002, Rene Schumann wrote:

> I have a Problem and hope someone here can help me.
> I have 2 Partitions on a drive.
> 
> [root@desktop root]# fdisk -l /dev/sdb
> 
> Festplatte /dev/sdb: 255 Köpfe, 63 Sektoren, 9730 Zylinder
> Einheiten: Zylinder mit 16065 * 512 Bytes
> 
>     Gerät Booten  Anfang      Ende   Blöcke   ID  Dateisystemtyp
> /dev/sdb1             1      4462  35840983+   c  Win95 FAT32 (LBA)
> /dev/sdb2          4463      9730  42315210   8e  Linux LVM
> 
> I want to delete sdb1 vfat partition and use it as LVM space.
> If i do a "pvcreate vg01 /dev/sdb1" it is ugly for performance because
> there are 2 LVM Partions at one drive.
> right?
> If i do lvm partition on sdb1 and do a pvmove,
> Can i resize sdb1 to fit the whole drive and after that lvm use this
> full space? 
> 

I don't think you can resize a PV, however that does not really matter,
just slap another PV in place of it. When you do a lvcreate you can
specify which PV the logical volume is going to take its space from.

lvcreate -n fred_lv -L 1G jim_vg /dev/sdb1

If you wanted to do a strip you can still do it by doing

lvcreate -i 2 -n jim_lv -L 1G shela_vg /dev/sdb1 /dev/sdc1

The only time you would have any difficulties is if you wanted one of the
strips to take from sdb1 and sdb2, if your using concatinated filesystems
it really does not matter that the data is logically in two PVs if you
care about seek orders just specify /dev/sdb1  /dev/sdb2 when allocating.

James

Re: [linux-lvm] Partitions on same Drive

[Patrick Caulfield]

On Mon, Jan 21, 2002 at 03:28:35PM -0600, mitch@mdmiller.com wrote:
> > if you don't create striped LVs on the two partitions i see no
> > significant performance problem.
> 
> Brings up a question ... can you get improved performance by striping to
> multiple devices on the same SCSI channel, or do they really need to be on
> separate SCSI channels for good performance?  Ex: I have a fibre channel
> card, and multiple drives I'm gonna hook up ... someday.  Can I strip
> across all the drives and expect to push fibre channel's capabilities?

This does work OK provided that you don't hit the transfer limit on the SCSI
channel. If you have a fast SCSI and slow disks then striping can be beneficial.
Even an Ultra160 SCSI disk is unlikely to be sending 160MB/s continuously (it
has to seek at some time!) so, in theory, you should get some benefit.

My much maligned (and rightly so) striping graph shows that striping on my
interface works well for up to 3 disks on one fibre-channel.

Try it...!

patrick