SAN Performance During Disk Levelling

[Ian Foster_2]

We have an EVA3000 with a 22x72GB disk group. We already have a 250 GB (VRAID1) VDISK exported to our rp7410 Unix server to host our database.

We are proposing to create and export an additional 300 GB VRAID1 VDISK on the SAN. My question is, is this configuration activity on the SAN likely to impact on performance on the Unix system ie. while disk levelling across the group on creating the new VDISK ?

What would be your recommendations ie. should this be done during a system outage, or while the system is quiet, or can it be done during normal operations without any major risk to performance ? I would have assumed that the management appliance will treat the configuration and associated levelling as a background activity, however the only experience I have of this since the system was first commissioned has been levelling following the replacement of single failed disks.

Any advice or experience here greatly appreciated.

[SAKET_5]

Ian,

Vdisk creation is an online process. Sure, this could potentially impact the storage array's performance in some regard but this should be extremely minimal and should not concern you at all. If one would have to schedule system downtime to create a Vdisk which is a fairly regular and mundane task for most of the organisations - it would be practically impossible to work with the technology.

Sure, even a background disk scan of many sorts performed automatically by many storage arrays at random time intervals where a user has no control could hamper performance of the controllers in some regard. All this should not be of any concern to you. Not even in the SA5i, 5i +, 6i, HSZ70, HSZ80, HSG80 and the MSAs world - so have no doubt...go ahead and create your Vdisks online on the EVAs.

[Sheriff Andy]

I have to agree with SAKAT,

Creating a vdisk should not have any problems during production hours. I would think that most likely no one would know that a vdisk was created unless you told them.

Depending on how many devices you have, an ioscan might have more impact then creating a vdisk on the SAN.

[Tom O'Toole]

I think there shouldn't normally be a leveling as a result of a vdisk creation. There will be disk activity to allocate space for the vdisk. If the system is showing signs of slowness during prime time, you could script the creation to run in the middle of the night.

[SAKET_5]

If you are having performance issues in creating a Vdisk on an EVA during any hours then I think you have BIGGER problems elsewhere that you seriously need to track down. I am not even going to start on the potential causes there...but fan out ratio, host port oversubscription, etc, etc...!!!

I am sure you have paid handsome dollars for your EVA - let it do what its meant to do - dont create any unnecessary work for you if you can avoid it...Vdisk creation is well and truly an online operation!..No debate there:)