Raid 5

From an exam prep question:

There are 9 scsi hard drives installed in server 2003. Disk 1 contains the o/s. Disk 2,5, and 8 are a Raid 5 volume. Disks 3,4, and 6 are another raid 5 volume. Disk 7 is a mirror to disk 1. Disk 9 is a single volume.

Which disks can fail at the same time but leave the server fully operational after a restart?

One answer gives disks 1, 2 and 5 failing at the same time which the book says is incorrect.

Why would it be incorrect, thought a failed raid 5 volume that doesn't contain system files would not effect the running of the system?

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Comments

alanier

the system would boot but disk 2 and 5 cant both fail and that raid 5 volume work. the question is not very clear but i believe they mean not just being able to boot the server.

astorrs

Either disk 1 OR 7 can fail
Any ONE of 2, 5 or 8 can fail
Any ONE of 3, 4 or 6 can fail
9 cannot fail as it has no redundancy

As long as no more than one of the disks in those above groups fails the server could sustain up to 3 drive failures.

RobertKaucher

Mikdilly wrote:

From an exam prep question:
Which disks can fail at the same time but leave the server fully operational after a restart?

Question is pretty clear. That server is not fully operational if you cannot get to resources on the RAID 5 volume.

Imagine you have a database server and the database files are on the RAID 5. Would your boss consider that server fully operational if the database files were gone? Would you tell your boss "but it boots?"

Edit: Man I sound like a jackass here, not trying to be. I promise!

My point is you have to understand the expectations of the question and here the "gottcha" is "fully operational."

Mikdilly

Thanks for the replies, at first I think I mis-interpreted the question, but in re-reading it I can see what they meant by 'fully operational'. Just thought they were asking whiich drive failures would take down the server(prevent it from booting).

94jedi

Mikdilly wrote:

Thanks for the replies, at first I think I mis-interpreted the question, but in re-reading it I can see what they meant by 'fully operational'. Just thought they were asking whiich drive failures would take down the server(prevent it from booting).

that's the hardest part about these tests. interpreting the questions and giving the answer based on the proper interpretation.

knowing the material is easy. being able to apply it in the face of a question under a time constraint is the key.