June 6, 2008 at 1:46 am
If you have 5 disks on RAID 5, and the scenario is if you want to save the 5 disks how many disks you will add?
the options are:
1.-----1 disk
2.-----2 disks
3.-----5 disks
4.-----10 disks
what is the correct answer!?
this is one question that I had on employment test!
June 6, 2008 at 3:00 am
I think if its anything other than 1 it would not be a RAID 5 solution.
Gethyn Elliswww.gethynellis.com
June 6, 2008 at 3:10 pm
Ellis RemoteDBA (6/6/2008)
I think if its anything other than 1 it would not be a RAID 5 solution.
Hmmm... can you explain more why just adding one disk and still in RAID 5, and what happened if you add more disks!
:w00t:
June 6, 2008 at 4:06 pm
RAID 5 is striping with parity.The one disk which Ellis is referencing will be your parity disk. Say if one disk fails. in that scenario, your data will be read by using the parity disk. But if two disks fails, you are out of luck and can't do anything. you need to remember that there is a cost for counting the parity disks. And rebuilding it is costly too in case of failures. What exactly are you trying to do ?
June 6, 2008 at 4:08 pm
definition of RAID 5 from wiki:
Striped set with distributed parity. Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive. SNIA definition
so adding 1 drive - using all 5 disks and leaving one for parity (6 in total)...if one fails you have a spare.
If you added two disks you get RAID 6:
Striped set with dual distributed parity. Provides fault tolerance from two drive failures; array continues to operate with up to two failed drives. This makes larger RAID groups more practical, especially for high availability systems. This becomes increasingly important because large-capacity drives lengthen the time needed to recover from the failure of a single drive. Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt: the larger the drive, the longer the rebuild will take. Dual parity gives time to rebuild the array without the data being at risk if one drive, but no more, fails before the rebuild is complete. SNIA definition
If you add an additional 5 drives you can use RAID 10 (striped + mirrored)
I may be completely worng mind...i'm sure i'll get shot down if i am.
I hope this helps...
Gethyn Elliswww.gethynellis.com
June 7, 2008 at 11:45 am
so the answer is 1 disk! Ok a didn't have any idea how many but I choos 2 disks in the logic that the RAID 5 should be with 3 or 5 or 7 disks! But I was wrong and I accept that I do not have professional experience with RAID configuration in advanced level! - for that reason I asked about correct question!
thnx anyway ElliotRemoteDBA
😎
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