LUSE 36 LDEV limit (trying to create 1.2TB LUN)

[DBruno]

Hi,

Hardware: XP24000 running FW v 60-04-13

I need to create a 1200GB (1.2TB) LUN. I have multiple volumes (all 25GB) available. With this size I would need 48 LDEV but LUN expansion only allows for 36 LDEVs max. I have enough allocated but unused volumes in the same CU that I could free up. Can you please advise on how to go about this?

Thanks!

[Bulent ILIMAN · Accepted solution]

What Emulation are you using?

Didn't you use OPEN-V ?

If OPEN-V is used than the best way is to convert the 25 GB LDEV's to larger ones, say 100 GB if possible and use 12 of them.

What is the size of your physical drives and which RAID level are you using?

[krusty]

I agree with "BulentILIMAN". LUSEing that many LDEVs together could cause a performance hit, as it is a concatenation of LDEVs. It fills tha first LDEV, then the second, and so forth. If you have a low amouont of used storage, it would only be on those LDEVs.

LUSEing that many LDEVs is really out-of date these days. Back when XP's used OPEN-3 and OPEN-8s and you needed large LUN sizes, that was the only way. Now with OPEN-V, you can size the LUNs to whatever size you want. You would still need some planning (you might want to still make a LUSE say from LDEVs spread all 4 ACPs, should that be possible in your environment (4x 300GB).

Cheers,

Curt

[DBruno]

Curt & Bulent, thanks for your replies. A few updates: emulation is OPEN-V and the disk size is 146GB, RAID 5 (7D+1). What you are both suggesting is exactly what what I want to do. How do I resize the LDEVs from 25G to 100GB? I tried VOLUME TO SPACE but then I can only seem to create CVs that are smaller than 25GB. I think perhaps my sequence is off. Can you please share a procedure or help me with the steps? Don't worry I'll make sure not to screw up anything :-)

Thanks again for all your help.

David

[Bulent ILIMAN]

A new LDEV can only be created if you have availabale space on the redundancy group.

If your disks are 146 GB then options are as follows,

in a 3D+1P condition your maximum LDEV size is ~400GB and minimum is 46 MB.


in a 2D+2D condition your maximum LDEV size is ~280GB and minimum is 46 MB.

in a 6D+2P condition your maximum LDEV size is ~800GB and minimum is 46 MB.


in a 7D+1P condition your maximum LDEV size is ~930GB and minimum is 46 MB.

I could not understand why you can not create larger LDEVs.

How many LDEVs have you created on a parity group. You need to convert four 25GB LDEVs VOLUME TO SPACE to have 100GB available space to create new 100GB.

[DBruno]

Hey guys, I followed your instructions and was able to increase the volume sizes and I now have my 1.2TB LUSE.

Once again, thanks a million for your help.

[krusty]

Glad we could help - don't forget to assign points!

Cheers,

Curt

[DBruno]

I just did.

Thanks again.

[jeevanandham]

Can anyone help me to understand  why LUSE has only 36 ldev limited, is there any specific reason for the limitations, let me know if other than perfomance issues

[tbone654]

The "whisper" number for performance is 6 or 7 LUSE volumes MAX. Beyond that the performance penalty is logrithmic.

With the relatively new pool and tier concepts, there is no reason to use LUSE anymore.

One other performance note... If you configure pools on HP P9500 or HDS VSP systems using RAIDCOM (command-line) be careful to assign the same VSD to each portion of a large raidgroup. the GUI will do this properly, but using RAIDCOM will go in sequence from 0 to 7 (max) and you will take a performance hit on each multi-cv raidgroup configured. You may not see the hit it on most systems, but if your a hedge-fund it could be a big problem.