one or multiple disk group on eva systems

[Nappyb6]

we have an eva3000 systems.

is it recomended to create multiple disk groups or group all disks under the default disk group ?

is it recomended to use single protection or double protection ?

[Pshedges]

This is the link to the Best Practices guide.

http://h71028.www7.hp.com/ERC/downloads/5982-9140EN.pdf?jumpid=reg_R1002_USEN

Usually a single disk group is best, but it will depend on what levels of RAID you require, what size disks you have (you do not really want to mix disk sizes), what performance you require etc.....


Disk protection level will depend on what level you want.
Single Level Protection 'Hides' 2 x Size of the largest disk in the disk group and Double 'Hides' 4 x the size of the largest disk in the disk group.
This just hides disk space to ensure that you have enough capacity available should you suffer multiple disk failures - this is ensures you do not end up in a situation where you have a disk failure and there is not enough space to rebuild the disk.

[DragomirAtea]

Hi!

There is three major reasons why you should consider more than one diskgroup...

1. Different sized disks
2. Different I/O patterns (random/sequential access)
3. Higher security by placing clones or snapclones on a different diskgroup in case of diskgroupfailure...

I'we got this reccomendations from HP
>24 diskdrives singel protection
<24 diskdrives double protection

Regards
Dragomir Zekic

[Amar_Joshi]

If you are sure that new diskgroup's vdisks will have very high IO demand and don't want to see a change in existing diskgroup's performance go with a separate diskgroup. There are overheads of having separate diskgroup:

1. You will loose 2 separate spare capacity (diskgroups can't share spares)
2. Highly recommended that leave 10 to 15% of space in each diskgroup. (other word don't use the full capacity of any diskgroup).

Advantage:
1. separate living area for both diskgroups and applications don't suffer if other diskgroup is going under maintenance, such as creation of vdisks and rebuild of diskgroup after any disk failure.


correction to Dragomir's recommendations:

<24 disks: single protection
>24 disks: double protection

Amardeep

[DragomirAtea]

Comment to Amar

Ooops!

My bad!!!