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which RAID level for write only?



 
 
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  #1  
Old September 15th 03, 03:21 AM
Tester A.
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Default which RAID level for write only?

I would like to know which raid level is the best for Write operation.
I am considering Raid 0, Raid 1 , Raid 0+1, Raid 10, Raid 3, and Raid 5.

Also, are there any Raid Storage support Raid4, except NetApp?

TIA


  #2  
Old September 15th 03, 07:19 AM
Mark
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It depends on if you actually want the Redundancy part of RAID, if you want
speed do RAID 0 (Stripe), if there is lots of sequential stuff then RAID 3
would be a safe bet.

Regards

Mark

"Tester A." wrote in message
...
I would like to know which raid level is the best for Write operation.
I am considering Raid 0, Raid 1 , Raid 0+1, Raid 10, Raid 3, and Raid 5.

Also, are there any Raid Storage support Raid4, except NetApp?

TIA




  #3  
Old September 15th 03, 08:31 AM
Tester A.
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Default

Yes, I need redundacy, so RAID 0 is not the option for me.
Also, the files that are written is email messages backup, which is very
small. This is the backup server, so not much read access is there, unless
the main server is broken.
Raid 3 is better than other levels for write operation?

"Mark" wrote in message
...
It depends on if you actually want the Redundancy part of RAID, if you

want
speed do RAID 0 (Stripe), if there is lots of sequential stuff then RAID 3
would be a safe bet.

Regards

Mark

"Tester A." wrote in message
...
I would like to know which raid level is the best for Write operation.
I am considering Raid 0, Raid 1 , Raid 0+1, Raid 10, Raid 3, and Raid 5.

Also, are there any Raid Storage support Raid4, except NetApp?

TIA






  #4  
Old September 15th 03, 10:27 PM
Malcolm Weir
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Default

On Mon, 15 Sep 2003 02:21:53 GMT, "Tester A."
wrote:

I would like to know which raid level is the best for Write operation.
I am considering Raid 0, Raid 1 , Raid 0+1, Raid 10, Raid 3, and Raid 5.

Also, are there any Raid Storage support Raid4, except NetApp?


RAID-4 buys you (as a consumer) nothing, and its presence in NetApp
products is an artifact of their development priorities/processes.

If your I/O operations are many and small, then either RAID-5 or a
stripe of RAID-1 (sometimes called RAID-10 by the marketroids) is what
you want. If they are few and large, you want (true) RAID-3. If your
performance following a drive failure is critical, RAID-3.

Simple math:

With N disks, the maximum number of simultaneous write ops is:

RAID-1: (N/2)
RAID-3: 1
RAID-4: 1
RAID-5: (N-1)/2

[ Obviously, in the case of RAID-3, the time taken for the write is
dramatically improved over the time taken by a single disk. In the
other cases, the write time is (very roughly) somewhere between one
and two times that of a single disk. ]

Malc.
  #5  
Old September 16th 03, 12:34 AM
Peter da Silva
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Default

In article ,
Malcolm Weir wrote:
RAID-4 buys you (as a consumer) nothing, and its presence in NetApp
products is an artifact of their development priorities/processes.


NetApp isn't really RAID-4 in the normal sense, is it? I was under the
impression that it was actually handled at the file system level.

--
I've seen things you people can't imagine. Chimneysweeps on fire over the roofs
of London. I've watched kite-strings glitter in the sun at Hyde Park Gate. All
these things will be lost in time, like chalk-paintings in the rain. `-_-'
Time for your nap. | Peter da Silva | Har du kramat din varg, idag? 'U`
  #6  
Old September 16th 03, 04:42 AM
idunno
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Default

On Mon, 15 Sep 2003 18:19:47 +1200, "Mark" wrote:

It depends on if you actually want the Redundancy part of RAID, if you want
speed do RAID 0 (Stripe), if there is lots of sequential stuff then RAID 3
would be a safe bet.

Regards

Mark


When should one choose RAID 3 over RAID 10? Both perform well.
  #7  
Old September 25th 03, 11:03 PM
Mark
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"idunno" wrote in message
...
On Mon, 15 Sep 2003 18:19:47 +1200, "Mark" wrote:

It depends on if you actually want the Redundancy part of RAID, if you

want
speed do RAID 0 (Stripe), if there is lots of sequential stuff then RAID

3
would be a safe bet.

Regards

Mark


When should one choose RAID 3 over RAID 10? Both perform well.


Cost would be a factor with RAID 10 you need more physical drives than you
would with a RAID 3 or 5 setup.

Mark


  #8  
Old September 28th 03, 07:17 AM
idunno
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Default

"Mark" wrote in message ...
"idunno" wrote in message
...
On Mon, 15 Sep 2003 18:19:47 +1200, "Mark" wrote:

It depends on if you actually want the Redundancy part of RAID, if you

want
speed do RAID 0 (Stripe), if there is lots of sequential stuff then RAID

3
would be a safe bet.

Regards

Mark


When should one choose RAID 3 over RAID 10? Both perform well.


Cost would be a factor with RAID 10 you need more physical drives than you
would with a RAID 3 or 5 setup.

Mark




RAID 5 is versatile all-around good performer (on good cards only I
might add) but is not the highest performer when it comes to writes.
RAID 3 and 10 are both intended for high throughput applications that
require fault-tolerance. Yes RAID 3 and 5 have a better ratio of ECC
disk space to data disk space, but I was wondering if there is also a
significant performance difference in disk writes or whether certain
environments prefer RAID 3 or 10 on a _strictly_ performance basis.
  #9  
Old September 29th 03, 12:10 AM
Bill Todd
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Default


"idunno" wrote in message
om...

....

RAID 5 is versatile all-around good performer (on good cards only I
might add) but is not the highest performer when it comes to writes.
RAID 3 and 10 are both intended for high throughput applications that
require fault-tolerance. Yes RAID 3 and 5 have a better ratio of ECC
disk space to data disk space, but I was wondering if there is also a
significant performance difference in disk writes or whether certain
environments prefer RAID 3 or 10 on a _strictly_ performance basis.


For small writes, a classic RAID-3 implementation may be slightly faster
because its spindles are synchronized (and the mirrored spindles in RAID-10
typically aren't, so the write there will take take the longer of the two
disk access times). But if the RAID-10 controller has stable write-back
cache such that it can queue up write requests and execute them in optimal
order, any such advantage may be reduced or eliminated (as it will be for
large writes in any event, where the access times become a smaller
percentage of the overall overhead).

But that's for purely serial small writes. For multiple small writes
requested in parallel, RAID-10 may well be able to process at least some of
them in parallel, whereas RAID-3 will serialize them at the parity disk
(though should at least be able to queue-optimize their execution).

RAID-10, of course, provides potentially significantly better *read*
performance for a given usable capacity. It also provides somewhat better
availability, since with RAID-3 (or -5) the loss of any two disks results in
data loss whereas with RAID-10 data is lost only if the two disks happen to
be partners.

- bill



  #10  
Old September 29th 03, 06:36 AM
idunno
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Default

"Bill Todd" wrote in message ...

For small writes, a classic RAID-3 implementation may be slightly faster
because its spindles are synchronized (and the mirrored spindles in RAID-10
typically aren't, so the write there will take take the longer of the two
disk access times). But if the RAID-10 controller has stable write-back
cache such that it can queue up write requests and execute them in optimal
order, any such advantage may be reduced or eliminated (as it will be for
large writes in any event, where the access times become a smaller
percentage of the overall overhead).

But that's for purely serial small writes. For multiple small writes
requested in parallel, RAID-10 may well be able to process at least some of
them in parallel, whereas RAID-3 will serialize them at the parity disk
(though should at least be able to queue-optimize their execution).

RAID-10, of course, provides potentially significantly better *read*
performance for a given usable capacity. It also provides somewhat better
availability, since with RAID-3 (or -5) the loss of any two disks results in
data loss whereas with RAID-10 data is lost only if the two disks happen to
be partners.

- bill


Thank you. That helps. Are these performance differences maintained
when you enable spindle sync on a RAID 10 array with a large
write-back cache?
 




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