Loose Disks

[simon_164]

I have an EVA 4000 with 2 disk enclosures. each disk enclosure have 11 disk so the total is 22 disks.
I have 2 disk groups:

1- 14 disks with vdisks configured as Vraid5. protection level of one. 7 disks in each enclosure.

2- 8 disks with vdisks configured as Vraid1. protection level of one. 4 disks in each enclosure.

I want to know how many disks can i loose and stay alive: have my vdisks presented and operating with no problems.
how many disks can i loose and be able to restore my data back.
we can assume two scenarios: I am very lucky or I am very unlucky.

I guess I am always very unlucky :( .

[Jaime Bolanos Rojas. · Accepted solution]

Hi Simon,

With the Raid 5 you can loose one drive, if you got something like a hot spare, you will be able to loose two as far as the second one does not go down during the building process of the hot spare.

With a mirror you can loose 1 too, same situation with the hot spare.

There is a nice array config call ADG, it will let you loose two drives at the same time, take a look at this site for more info:

http://www.acnc.com/04_01_06.html

Regards,

Jaime.

[raadek]

It slightly diffrent in EVA world though.

EVA will always try to rearrange array layout if a disk fails. Hence if you have plenty of space you can have more failed drives than 'guranteed' number but still not loose your data.

Protection level 1 means that a distributed capacity of a single drive is reserverd as a hot-spare area. In Vraid5 you can tolerate a failure of one drive due to parity calculation. If the second drive fails AFTER rebuliding has completed (using spare capacity) then again - no data loss.

Vraid1 is an equivalent of traditional RAID10, where you can loose up to half of you drives IF one drive from each mirrored pairs remains working (but if you are unlucky a failure of only 2 drives from the same mirror pair will cause data loss).

Protection level rule still applies - it works like one (or more) hot spare drives.

Rgds