topic Re: max EVA disk fail in Disk Enclosures

max EVA disk fail

tommy_28 — Wed, 01 Dec 2004 01:34:30 GMT

Hi,

I'm curious to know what is the max number of concurrent physical disk(s) failure that EVA can tolerant.

Since RAID0 can hold zero failure, RAID1 - half failure, RAID 5 - one failure. What is about the VRAID1/5? That also means, what is the data store policy for EVA?

Thx.

Re: max EVA disk fail

Stf — Wed, 01 Dec 2004 05:36:40 GMT

Hello,

as it says in the following document :

http://www.pcguide.com/ref/hdd/perf/raid/levels/multLevel15-c.html

"The fault tolerance of these RAID levels is truly amazing; an eight-drive RAID 15 array can tolerate the failure of any three drives simultaneously"

Stf ;-)

Re: max EVA disk fail

Alzhy — Wed, 01 Dec 2004 10:06:28 GMT

THATS what the manual sez ;^).

But judging from experience.. EVA's even if it has the word "Enterprise" on it - believe me, are not robust single array solutions compared to the EMC, the IBM Arrays or the Hitachi arrays (which HP OEM's as the XP series).

If you've deep pockets - keep another EVA handy and mirror accross the 2.

Re: max EVA disk fail

tommy_28 — Wed, 01 Dec 2004 21:21:19 GMT

EVA VRAIDs are different to traditioanl RAIDs, anyone can give me VRAID fault tolerant informations?

Re: max EVA disk fail

Karsten_4 — Thu, 02 Dec 2004 03:37:17 GMT

Hello

The EVA Array can only Raid1 or Raid5 for one LUN (not RAID15). Each LUN can have different Raid Levels using the same Disks (Virtuel Array)

Internaly the EVA groups the Disks in smaler Groups (RSS whith 8-12 Disks)In every one Group one Disk can fail at one Time.
To get realy high available Configurations you need an EVA 5000 whith min. 8 Shelfes.
When you then put your Disk evenly across all shelves the EVA 5000 can tolerate an hole shelf failure.
Hope this helps.

Re: max EVA disk fail

WilliamSmith11 — Thu, 02 Dec 2004 09:51:54 GMT

Tommy you have the docummetation EVA best Practice?
I can send it to you.
Tell me if will be fine for you.

In the lab I do some test copying data.
while the system was copying data I pull out three disk in the disk group and the system continue working.

That is my experience but I said in the lab.

Re: max EVA disk fail

Mike Naime — Thu, 02 Dec 2004 20:00:25 GMT

Well, we pulled an entire shelf from one of our 2C18D EVA5000 configurations (14 drives) and it's still running. The shelf/bus was a lemon, and we are in the process of migrating all data off that EVA and onto other storage controllers so that we can send it back to HP for analysis.

To really answer your question, you have to look at the folowing:
Total number of disk groups.
How many disks per disk group.
Sparing level on each disk group.
Occupancy level for that disk group.

Basically because the EVA spreads the data for the entire disk group across all of the disks in that disk group. You can loose as many disks from that particular disk group as you have free space in that group. (assuming that you have enough time for leveling to occure between failures.)

IF you are at 90%+ occupancy level, you can only loose a few drives before you are at 100% occupancy. :-(