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More drives = faster RAID 5 ?



 
 
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  #1  
Old October 1st 03, 10:20 AM
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Default More drives = faster RAID 5 ?

I've question regarding RAID 5, is there any benefit in going beyond 3 hard
disks when you're using RAID 5 ?.

Obviously if you need huge amounts of storage then 'yes' but if you have
modest storage requirements (say 8 GB) and need faster read/writes is there
any benefit from having more disks ? (or should I just ignore RAID 5 and use
RAID 10 instead ?).

Thanks.

Clive.


  #2  
Old October 1st 03, 10:29 AM
Bill Todd
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Default


wrote in message
...
I've question regarding RAID 5, is there any benefit in going beyond 3

hard
disks when you're using RAID 5 ?.


Yes: more capacity, better performance.


Obviously if you need huge amounts of storage then 'yes' but if you have
modest storage requirements (say 8 GB) and need faster read/writes is

there
any benefit from having more disks ? (or should I just ignore RAID 5 and

use
RAID 10 instead ?).


Can you actually find disks smaller than 8 GB any more? If not, and a
mirror pair will give you the performance you need, why consider RAID-5 at
all?

Read performance is pretty much linear in the number of disks you use,
whether they're organized as RAID-5 or RAID-1/10. Write performance will
usually be better with RAID-1/10 than with RAID-5 (though very large writes
won't see much difference either way, if your RAID controller is smart). A
RAID controller with stable write-back cache will often improve small-write
performance more than adding disks will (this will definitely be true if
your write workload is serial rather than parallel in nature), but if the
controller's write-back cache isn't itself mirrored it constitutes a single
point of failure that is otherwise avoidable.

- bill



  #3  
Old October 1st 03, 11:02 AM
external usenet poster
 
Posts: n/a
Default

Thanks for the v. helpfull reply Bill.

Clive.

"Bill Todd" wrote in message
...

wrote in message
...
I've question regarding RAID 5, is there any benefit in going beyond 3

hard
disks when you're using RAID 5 ?.


Yes: more capacity, better performance.


Obviously if you need huge amounts of storage then 'yes' but if you have
modest storage requirements (say 8 GB) and need faster read/writes is

there
any benefit from having more disks ? (or should I just ignore RAID 5 and

use
RAID 10 instead ?).


Can you actually find disks smaller than 8 GB any more? If not, and a
mirror pair will give you the performance you need, why consider RAID-5 at
all?

Read performance is pretty much linear in the number of disks you use,
whether they're organized as RAID-5 or RAID-1/10. Write performance will
usually be better with RAID-1/10 than with RAID-5 (though very large

writes
won't see much difference either way, if your RAID controller is smart).

A
RAID controller with stable write-back cache will often improve

small-write
performance more than adding disks will (this will definitely be true if
your write workload is serial rather than parallel in nature), but if the
controller's write-back cache isn't itself mirrored it constitutes a

single
point of failure that is otherwise avoidable.

- bill





  #4  
Old October 1st 03, 09:53 PM
David Magda
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Posts: n/a
Default

writes:

I've question regarding RAID 5, is there any benefit in going
beyond 3 hard disks when you're using RAID 5 ?.

[...]

Well, you can setup a fourth as a hot spare in case one of the first
three dies.

--
David Magda dmagda at ee.ryerson.ca,
http://www.magda.ca/
Because the innovator has for enemies all those who have done well under
the old conditions, and lukewarm defenders in those who may do well
under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI
  #5  
Old October 6th 03, 04:15 PM
Calphurn
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Default

I think more disks will result in higher performance because read/write
access is parallel based on strap.
raid5 sacrifices one disk to guarantee the data security. Alternatively,
raid10 will be expensive but more save.

дÈëÓʼþ ...
I've question regarding RAID 5, is there any benefit in going beyond 3

hard
disks when you're using RAID 5 ?.

Obviously if you need huge amounts of storage then 'yes' but if you have
modest storage requirements (say 8 GB) and need faster read/writes is

there
any benefit from having more disks ? (or should I just ignore RAID 5 and

use
RAID 10 instead ?).

Thanks.

Clive.




 




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