Re: [Xen-users] iscsi initiator on PV DomU problem

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Mon, Mar 9, 2009 at 10:38 PM, Longina Przybyszewska
<longina@xxxxxxxxxxxx> wrote:
>> First of all, I believe you'd get better performance if the initiator
>> is on dom0 instead of domU.
>>
>
> It seems that management could be easier if there are multiple iscsi
> targets.
>
> My iscsi targets get their own PVM and they access it through bonding
> interface with vlan and transparent bridge on top of it - IP address is set
> first for PVM.

Sometime ago on this list (check the archive) a user said iscsi on
domU was slow, and moving the target to dom0 improved performance
greatly. But it seems like you know what you're doing, along with its
consequences :)

>> Probably because there's already a partition table on that block
>> device, and it's messed up (maybe because the block the device was
>> used previously, and then shrinked).
>
> This is probably what happened - how could be this avoided?

By using a "fresh" SAN :)

Traditional SAN might present "garbage" data (in your case the
partition table) if the target was previoulsy used on another host.
zfs-based SAN/NAS (like the new SUN 7000-series) is somewhat unique in
that each time you create a volume (zvol) it will be blank (no data
from previous use).

You could always write all zeroes to it with dd and get a similar result :)

>
>>
>> What does "cat /proc/partitions" and "fdisk -l /dev/sda" shows?
>
>
> cat /proc/partitions:
>
> 8       0       314573823 sda
> 8       1       488319741 sda1
>

Just to make sure: you onlye have ONE disk, right? Not two disk, one
mapped as sda and another as sda1 (which is possible when using xen)?


> fdisk -l /dev/sda:
>
> Disk /dev/sda: 322.1 Gb 322123595264 bytes
> 255 heads, 63 sectors/track, 39162 cylinders
> Units = cylinders of 16085 * 512 = 8225280 bytes
> Disk identifier: 0x00000001
>
> Device   Boot   Start   End     Blocks          Id      System
> /dev/sda1        1      60783   488319741       83      Linux
>

If you only have one disk, this is a mess. Your disk has 39162
cylinders, but the first partition uses 60783 cylinders.

>>
>> If it is indeed messed up partition table, you can use fdisk's extra
>> functionality to change the number of heads, sectors/tracks, or
>> cylinders.
>
> Is it that one - "use it if you know what are you doing ?" :)

Yup :)

> How can I find out about the target's type -

Your setup seems to be simpler though, since sda is correct and only
sda1 is messed up.
If this is an empty (new) disk I believe you can simply use fdisk to
delete the first partition and create another one.

Regards,

Fajar

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