Solved

Why align a virtual lun

Posted on 2010-09-21
3
647 Views
Last Modified: 2013-11-14
Hi,

The need of aligning a raw lun or ISCSI lun  I understand.
But why align a virtual lun, it is just a file.

0
Comment
Question by:MTasova
3 Comments
 
LVL 2

Assisted Solution

by:madan1278
madan1278 earned 100 total points
ID: 33723672
If the virtual lun resides on a shared storage, the VM can be failed over seamlessly via the vmmotion network.
In a virtual lun acts like a physical to the actual VM's.
0
 
LVL 55

Accepted Solution

by:
andyalder earned 200 total points
ID: 33723728
The virtual KUN may be just a file but files are made up of blocks and clusters and these should be aligned to an even boundary to avoid split I/Os. See the drawing on page 5 of http://www.vmware.com/pdf/esx3_partition_align.pdf. (it can get even worse if the SAN LUN itself is a file under iSCSI target software, then there's yet another layer where mis-alignment can occur)
0
 
LVL 10

Assisted Solution

by:BloodRed
BloodRed earned 200 total points
ID: 33724515
Essentially, it is still a file which is accessed by looking up the associated blocks on the underlying disk subsystem.  If the file is alligned, one virtual block will (well, should) map to one physical block and one I/O operation is used to read it.  If the virtual blocks are mis-aligned and span multiple physical blocks, each 'read' of a virtual block will require the disk head to read multiple physical blocks.  In other words, there will be more read/write operations required to write a single virtual block of data should the file be mis-aligned.
0

Featured Post

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

When converting a physical machine to a virtual machine using VMware vCenter Converter Standalone or vCenter Converter Enterprise, if an adapter type is not selected during the initial customization the resulting virtual machine may contain an IDE d…
The question appears often enough, how do I transfer my data from my old server to the new server while preserving file shares, share permissions, and NTFS permisions.  Here are my tips for handling such a transfer.
Teach the user how to configure vSphere Replication and how to protect and recover VMs Open vSphere Web Client: Verify vsphere Replication is enabled: Enable vSphere Replication for a virtual machine: Verify replicated VM is created: Recover replica…
This Micro Tutorial will teach you how to reformat your flash drive. Sometimes your flash drive may have issues carrying files so this will completely restore it to manufacturing settings. Make sure to backup all files before reformatting. This w…

830 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question