EVA 3000 - introduction of a larger disk size into a diskgroup.

[Christian Schwartz-Søre]

If you have a default diskgroup of 16 x 72 GB drives.
Protection level of "single".
Several Vraid 5 LUNS.
Spare capacity in the diskgroup.

You now do a test where you pull a single drive from the diskgroup - you then insert a 146GB drive. What will happen to the diskgroup ?

What will happen to the diskgroup if you, once the system has stabilized itself, remove the 146Gb drive and reinsert the old 72Gb drive again ?

Does anyone know ?

Regards
Christian

[Vladimir Vybiral · Accepted solution]

Hello,

1. pulling a drive from a disk group the array starts to rebuild the data into the protection space.
2. putting a bigger drive into the slot does nothing - You have to include it to the disk group in the management. The disk slot does not belong to the disk group after the rebuild has passed.
3. Having a diskgroup with just one bigger drive
a) works okay with no functionality impact, except:
b) reduces Your capacity as the protection level "single" means reducing by a space of twice the largest drive in the array / so instead of losing 2x73GB You lose 2x143GB - so You do not gain capacity, You lose it in case of one drive only
c) will create a performance hotspot on the drive as it will actually hold more data than the other drives in the group (this is the magic of EVA virtualization)
d) the nice thing is that EVA is handling all this and even in a case of failure all data will be rebuilt.

hope this helps, tell me if You want more :)

Vladimir

[Christian Schwartz-Søre]

Good answer V. Thanks.

What would happen if the single larger drive were removed, and the original 72Gb drive reinserted ?

Proposed answer:
Data would be protected and rebuilded, and the system returned to its original state ?

Or what's your view ?

Regards
Christian

[Antonio Gonzalez_4]

Christian, maind this: whenever you want to remove a disk drive, never unplug it first.
What you must do is to "Ungroup" the disk from the Command View first, and after you see the disk as "Ungrouped" and no warning in the EVA, you can then unplug the drive safely.

If you want to exchange you big drive by one normal size drive, you must:
1.- ungroup the big drive
2.- unplug the drive
3.- after 2 minutes, plug the small one where you like
4.- after 2 minutes add this drive to your group. For the EVA this drive is a new one, it got initialized and then inserted in the group for storing data as the others disks already in the same group.
5.- wait for the leveling phase to finish and review space, hardware, etc. to see that everything is OK

This way you will again use the spare size that you used before (2 * 72GB).
Remember to provide always some free space (at least 10 or 5%) apart from the spare reserved space.

If you monitor your EVA carefully, you also could change your Protection level (spare space) to none and add these GB to the free space. In case of disk failure, the EVA will rebuild the data using this free space.

[Uwe Zessin]

>Data would be protected and rebuilded, and the system returned to its original state ?

No. Definitely not. The EVA does not work like the SmartArray controllers. There is no 'previous state'. Once you have removed a disk through an unplug operation it is completely forgotten by the EVA.

If you plug the same disk back the EVA beleives it is a new disk and acts the same way as if you have put in a different disk.

[Kay Nally]

Christian

Can you explain to me what you mean by:

c) will create a performance hotspot on the drive as it will actually hold more data than the other drives in the group (this is the magic of EVA virtualization)

Thanks