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...

-- 
Steven Haigh

Email: [log in to unmask]
Web: http://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897