1006111 - ubuntu kickstart needs to generate aligned VMs

Status: RESOLVED FIXED

(Infrastructure & Operations :: RelOps: Puppet, task)

Description

[Chris Knowles [:cknowles]]

Per https://mana.mozilla.org/wiki/display/SYSADMIN/VMDK+Alignment - vm alignment is an important performance issue both for the individual VM as well as for the entire netapp filer environment.

Noticed when working bug 1002792 that the resultant VM of a puppetagain was not completely aligned.

# /opt/ontap/mbrscan taras-ubuntu1.relabs.releng.scl3.mozilla.com-flat.vm
dk 
mbrtools esxi version 1.0
 
--------------------
taras-ubuntu1.relabs.releng.scl3.mozilla.com-flat.vmdk p1 (Linux)       lba:2048        offset:1048576  aligned:Yes
taras-ubuntu1.relabs.releng.scl3.mozilla.com-flat.vmdk p2 (EBR )        lba:67110910    offset:34360785920      aligned:No
taras-ubuntu1.relabs.releng.scl3.mozilla.com-flat.vmdk e1 (swap)        lba:67110912    offset:34360786944      aligned:No

The extended and swap partitions aren't aligned.  Now, in day-to-day this isn't drop dead if this is all there is, as hopefully swap won't be used that much.  

However, if the landing of P1 at an aligned boundary is luck, then this could be problematic.

per netapp:

Linux OS 
To determine the alignment on Linux: 
# fdisk -lu 

In the output for each device, multiply the start by sector size (normally 512 in the fdisk output), and then divide it by 4096. If the result is an integer (whole number), it is ALIGNED, if not, it is MISALIGNED. 

Example with both aligned and misaligned partitions: 
# fdisk -lu


Disk /dev/sda: 21.4 GB, 21474842112 bytes 
255 heads, 63 sectors/track, 2610 cylinders, total 41943051 sectors 
Units = sectors of 1 * 512 = 512 bytes 
Device Boot Start End Blocks Id System 
/dev/sda1 * 64 208845 104391 83 Linux 
/dev/sda2 208856 41929660 20860402+ 8e Linux LVM 
/dev/sda3 * 63 208845 104391 83 Linux 
sda1: 64 * 512 = 32768 / 4096 = 8 so is ALIGNED 
sda2: 208856 * 512 = 106934272 / 4096 = 26107 so is ALIGNED 
sda3: 63 * 512 = 32256 / 4096 = 7.875 so is MISALIGNED

obviously, and per IRC, I'm happy to be of help testing/troubleshooting/suggesting solutions.  I'll need some newbie help finding the puppetagain kickstart files.

CJK

Comment 1

[Dustin J. Mitchell [:dustin] (he/him)]

I misspoke slightly in irc.  For *CentOS*, I've observed VMs to be created in an aligned fashion.  So this issue may be limited to Ubuntu kickstarts.

The kickstart profile for all PuppetAgain installs is in infra puppet at
  modules/pxe/templates/kickstart/profiles/puppetagain.erb
if you want to have a look and make a fix.  I can take a look when I'm back, too.

Comment 2

[Chris Knowles [:cknowles]]

aren't you supposed to be dispensing justice?  :)

I'll take a look, though I'm having trouble finding documentation for partman.  

Should have been clear - observed this in the ubuntu kickstart, wanted to make sure that we weren't accidentally stressing things all over.

CJK

Comment 3

[Dustin J. Mitchell [:dustin] (he/him)]

clearpart --all --initlabel
part / --fstype ext4 --size=1024 --grow --asprimary
part swap --fstype swap --size 4096 --asprimary

seems to work -- I'll land that.  I've re-imaged dustin-test, if you want to verify.

Comment 4

[Dustin J. Mitchell [:dustin] (he/him)]

over to you for verification

Comment 5

[Chris Knowles [:cknowles]]

# /opt/ontap/mbrscan dustin-temp-flat.vmdk 

mbrtools esxi version 1.0
 
--------------------
dustin-temp-flat.vmdk p1 (Linux)	lba:2048	offset:1048576	aligned:Yes
dustin-temp-flat.vmdk p2 (swap)	lba:75884544	offset:38852886528	aligned:Yes
--------------------

So, yes, that one's aligned.  I don't see anything in the commands that forces start sectors, which would be where the alignment gets forced.  So I'm not convinced we're not just lucky.

Thoughts?  Comfort for a paranoid sysadmin?

CJK

Comment 6

[Dustin J. Mitchell [:dustin] (he/him)]

Well, the size of the first partition is alignment-friendly.  So I think this should be reliable.  It's what we're doing on CentOS.

Comment 7

[Chris Knowles [:cknowles]]

Alrighty then.  Thanks for the explanation and the effort.  

CJK