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Is RAID10 the best?

I am have heard that RAID 10 is now the best and recommended by MS for everything. My understanding is that RAID10 is essentially, two pairs of mirrors, thus requiring 4 drives.

Is this true? I know the MS previously recommended RAID5?

Is RAID10 now the best for any sort of applcation, regardless of it's behaviour.
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neil4933
Asked:
neil4933
1 Solution
 
Duncan MeyersCommented:
RAID 10 is a RAID 0 stripe across multiple mirrored pairs.

The best RAID type depends on your application and requirements. For a given workload, RAID 10 often needs fewer drives than a RAID 5 set because of write penalties, but RAID 5 gives you more space for a given number of drives.

So - the answer is: it depends.  :-)
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wolfcamelCommented:
raid 10 tends to give the best overall performance for reading and writing data - but you lose half your capacity.
some raid configurations can be faster at reading and slower at writing data which may have its application.
for 99 out of 100 people Raid 10 is the choice.
check out..
http://www.petri.co.il/raid-levels-comparison-guide.htm
http://en.wikipedia.org/wiki/Standard_RAID_levels 
and http://www.midwestdatarecovery.com/raid-array-types.html
for more details
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Duncan MeyersCommented:
I wish it was that simple. It really depends on the workload and your requirements.
(The following assumes a SAN array or quality RAID controller):
For example, a RAID 5 set of 5 drives will have superior write performance for a 256kB write. It will have similar read performance to a 4 drive RAID 10 set. The RAID 10 set will outperform the RAID 5 set for small block random I/O.

Like I say: it depends.
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andyalderSaggar makers bottom knockerCommented:
Perhaps you could ask whether RAID 10 is superior to RAID 5 when one of the disks has failed. RAID 5 is often virtually unusable with a failed disk until rebuilding is complete.
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pgm554Commented:
>RAID 5 is often virtually unusable with a failed disk until rebuilding is complete.

Not an absolute.
You will take a performance hit,but if you have more than 3 spindles,that is not written in stone.
You also would need to factor in whether or not the RAID controller has a co processor too.

Good RAID controllers bypass having to use CPU resources(although I have heard it argued that using a core on a CPU alleviates this.)  .

None the less it does eat up CPU cycles one way or the other.


I've had disks fail and rebuild in more than one system,and production was just fine and usable

I could see if you were running RAID 5 software with 3 SATA TB hardrives and it becoming slow as they rebuild.

You also take a chance that if you lose a 2nd drive,your data is hosed.

Quite troubling considering that your bit rate error on larger drives grows exponentially the larger they become ,and if you hit a double bit parity error,ugh!

Speaking of RAID,it appears as if MS has fired a shot over the bow of NetApp and it's ilk.with something in Server 2012/W8 called Storage Spaces.

We'll see.
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neil4933Author Commented:
Thanks everyone...

So let's take Exchange as an example -

Exchange logs are heavy on sequential writes
Exchange DB is heavy on random reads

UP until now, the thinking has been to put behaviour like the logs on a RAID1, and behaviour like the DB on a RAID5.

Why does RAID10 suddenly seem like the best, that is what I'm trying to get at? Are we saying that because disks are now so cheap, RAID10 is viable?
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Duncan MeyersCommented:
The following assumes a smart RAID controller on storage array that has RAID 5 write optimisations
Sequential writes: RAID 5
Random reads: Either RAID 5 or RAID 1/0. Depends on space requirements

If your RAID controller (or SAN storage) is as dumb as a bag of hammers, then go RAID 1/0 for both.

>Why does RAID10 suddenly seem like the best, that is what I'm trying to get at? Are we saying that because disks are now so cheap, RAID10 is viable?
Here's an example. Let's say you have an environment that's generating 5000 IOPS, 66% reads, 34% writes, highly random:
First step is to calculate the workload at the disks:
RAID 5 (write penalty is 4):
Write workload:
(5000 x .34) x 4 = 6800 IOPS
Read workload
5000 x .66 = 3300 IOPS
6800 + 3300 = 10,100 IOPS
Assume 15K SAS drives @ 200 IOPS per drive. You need:
10,100/200 = 51 drives to handle the workload
Assume 7200 rpm SATA drives @ 80 IOPS per drive:
10,100/80 = 127 drives

Now for RAID 1/0 (write penalty is 2)
Write workload:
(5000 x .34) x 2 = 3400 IOPS
Read workload
5000 x .66 = 3300 IOPS
3400 + 3300 = 10,100 IOPS
Assume 15K SAS drives @ 200 IOPS per drive. You need:
6,700/200 = 34 drives to handle the workload
Assume 7200 rpm SATA drives @ 80 IOPS per drive:
6,700/80 = 84 drives

Now for RAID 5 sequential (write penalty is 1.25)

You can use these formulas to work out ratios for performance calculations. Note that you can consider a 64KB write or larger to be sequential.

Write workload:
(5000 x .34) x 1.25 = 2125 IOPS
Read workload
5000 x .66 = 3300 IOPS
2125 + 3300 = 5425 IOPS
Assume 15K SAS drives @ 200 IOPS per drive. You need:
5425/200 = 28 drives to handle the workload
Assume 7200 rpm SATA drives @ 80 IOPS per drive:
5425/80 = 68 drives

Let's do SSDs for fun:

Write workload:
(5000 x .34) x 4 = 6800 IOPS
Read workload
5000 x .66 = 3300 IOPS
6800 + 3300 = 10,100 IOPS
Assume  SSD drives @ 3000 IOPS per drive. You need:
10,100/3,000 = 4 drives to handle the workload

... and all your performance problems go away. Now all you need is space. Enter EMC FAST, NetApp Flash Cache, Compellent, etc etc

So as you can see in some cases RAID 5 is most economical, in others, RAID 1/0.
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