eva4400 new disk: add to existing group or create new group?

[pincholo]

running an EVA4400 with 2 disk enclosures

enclosure1 : 

8 disks FC450-15K

4 disks FC400-10k

enclosure2 : 

8 disks FC450-15K

4 disks FC400-10k

diskgroup1: 4 disks FC450-15k enclosure1 + 4 disks FC450-15k enclosure2

diskgroup2: 4 disks FC450-15k enclosure1 + 4 disks FC450-15k enclosure2

diskgroup3: 4 disks FC400-10k enclosure1 + 4 disks FC400-10k enclosure2

Installed a new disk enclosure with 8 FC600-15k disks

Would it be "better" to add the new disks to existing disk groups or to create a new group?

Looking for recommendations pros/cons

Most of the load is VMware virtual machines and database

thanks

[Johan Guldmyr]

Hi,

Why do you have 450GB 15k disks in two disk groups?

The EVA likes to have the disks in a disk group dividable by 8.
If you put 4 of the 600GB disks in DG1 and 2 you will get some background activity on the EVA - separating each DG into two RSS of 6 disks in each.

Also in the 600GB disks will have more data on them, (same % as the 450GB) but this means that they will also be used more than the 450GB disks and might be limiting the performance of that disk group.

So let's say you're using 50% of the available space in DG1 after you've added the 600GB disks. This means you have 225GB available on the 450GB and 300GB on the 600GB.

As you already have separated disk groups I would continue with it.

One negative side of keeping separate disk groups is that you do get less disk space for your bucks - especially if you have disk drive protection on.

If you have mixed sizes in a disk group, the drive protection will take 2x the space of the largest disk.

Also are you running vraid1? I'm not 100% sure on this but what if after you add the 600GB disks to the DG - you get a mirror pair with a 450GB disk and a 600GB disk. Probably you won't be able to use the whole 600GB disk then..

[pincholo]

The EVA started with 1 enclosure and 8 disks. This being mostly an IBM shop I dont think there was not much tougth put into it growing too large. Performance and feautures were good some another 8 disks were bougth. Then another enclosure and more disks.

Pretty much each disk group represents and expansion with new disks. Im trying to figure out how to improve the current setup.

So it seems that considering the new disks are diferent from the rest a new disk group with those disks would be a good choice. Do you think merging the 2 DGs of FC450-15k disks would be recommendable?

Thanks for the information.

[Johan Guldmyr]

If you do merge the two 450G DGs you theoretically get a pretty nice performance boost and if you use drive protection you'll also save some space. I'd say if you have the possibility you should merge them. 

[pincholo]

Sounds good. Is there any issue/trade-off if I move everything off from one of the FC450 DG , ungroup those disks and then add them one by one to the other FC450 DG ?

Or is it requiered to ungroup both disk gropus to make a new one ?

thanks for your help