On 10/23/2014 09:05 PM, Steven Haigh wrote:
> On 24/10/2014 1:59 PM, Orion Poplawski wrote:
>> On 10/22/2014 03:23 PM, Steven Haigh wrote:
>>> Hi all,
>>>
>>> I'm wondering - I'm looking to simplify my Xen DomU installation via a
>>> kickstart file...
>>>
>>> As my Xen config has /dev/xvda - which should be formatted as ext4 and
>>> used as / - is there any options that I can achieve this?
>>>
>>> Just about everything I've stumbled across does partitioning first - and
>>> not the entire disk. Without supplying a kickstart file, the installer
>>> will bail saying no disks found.
>>>
>>> It's been this way for MANY years, but I heard rumours of a magical
>>> kickstart option - but I can't seem to find it...
>>>
>>
>> What do you have against partitioning the disk?  Loosing the 512-bytes
>> for the partition table?
>
> On some setups it can cause major write degradations in the virtual machine.
>
> If you can imaging the disk being set up in 4Kb clusters - which LVM
> then adheres to - but on the DomU disk with a partition, the alignment
> for partition data is now 0 + 512 bytes instead of 0.
>
> This means a write of 4Kb would write two sectors to the physical disk
> (first being 512 bytes + 4Kb, the second being the 512 bytes that give
> us an offset).
>
> In lame ASCII art, this means:
>
> Plain Disk:
> 0-----------512-----------1024-----------1536-----------2048 etc
> Whole disk write:
> ----------------------------------------------------------> to 4Kb
> Partitioned disk write:
> [  part tbl  ]--------------------------------------------> to 4Kb + 512
> bytes
>
> Its good to get your sectors aligned.... Especially when its on a RAID
> backend that also has a stripe size as well...
>

Hmm, that is an issue.  I assume you've tried:

part / --onpart /dev/xvda

You may also be able to partition in %pre manually with GPT or dos with 
your desired alignment.

Having tried using full disk for things like md raid and lvm in the past 
an gotten burned by loosing most autodetection I've given up on not 
partitioning.

-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA/CoRA Division                    FAX: 303-415-9702
3380 Mitchell Lane                  [log in to unmask]
Boulder, CO 80301              http://www.cora.nwra.com