no to the data ..but i would do it during your very low IO times ..not to impact production performance.

Hi Sandip

Yes I do. I have about 100GB of free disk space that I can't use unless I defrag the RAID Group.

To my understanding it will not - but definitely it will affect the performance. Do you really need to defrag the RAID group?

Thanks,
Sandip

Ok. I 'll prefer to run this defragmentation during very low IO period - may be during the weekend, so that the impact on performance will be minimized.

It depends on how big your Raid Group is and what type of drives (FC or SATA).

Another point, I'll check that there is no trespassed LUNs and all the hosts accessing the LUNs on this RAID group are working properly without any failover or trespassing issue - as RAID group defragmentation in conjunction with trespassing may result in defragmentation process hanging (See Primus solution - emc88367 and emc152201).

You may contact EMC CLARiiON support, if required, for help or clarification.

Thanks,
Sandip

I've used the following trick on a RG with a somewhat larger number of LUNs:

suppose there's a "gap" in the beginning of the RG and the rest of free space is on the end. Let's asume the gap 35GB and in the end you have a 35GB LUN. Creating a new 35GB LUN in the this RG will place it exactly in the gap. Now choose migrate and choose the 35GB LUN in the end and let it migrate to the newly created "gap LUN". The outcome will be that the 35GB LUN is gone from the end has moved to the gap in the beginning of the RG. Instead of having to move hundreds of GB's, only 35GB had to be moved. The identity of the original 35GB LUN hasn't changed and this can also take place online. And it's quicker than having to defrag thwe whole RG !

But: you need to make sure that you can move the 35GB LUN (in my example), because having it in the end of the RG might have it's reasons performancewise.

hehe..very clever ..migration performance will probably be horrible (reading/writing same spindles) but like you said still better then defraging hundreds of gigs. I gotta try it next time ...Thanks for sharing

sure saves a lot of time.....

Defragmenting the raid group does effect performance on the san, but please realize the different levels that are associated with it. You can run it on low, medium or high. I have run it on high during low I\O periods and switched it to low when needed.

Sanadmin007,

I must disagree with your comment: running a defrag does not have any impact on the SAN at all since there's no data going over the SAN. The whole process takes place within the clariion itself, so the only thing you might notice is perhaps a slight performance degradation when running in low or medium setting. If running the defrag on high or ASAP, you most likely will notice the performance degradation. So run it in a low IO time, like in the evening or the weekend.

Btw: welcome to the forums !


PS A SAN is the FC network (Storage Area Network), not the storage array attached to the SAN !

This is an old thread but need some help. The primus states to disable trespassing on the RG or LUN (something like that). However, i do not see this option. I contacted EMC and they are also looking on how to do this.

So, I want to be proactive and follow the recommended steps in the Primus, however I don't see how this can be done.

I have clones which follow the souce luns, hence trespassing. I do not want to defrag until I get clarification on the primus and risk. I have a CX700 with Flare 24.17.

Anyone???

Thx.