disk sizing for build ms sql server databases server


I hae to setup 2 ms sql server instances on a windows server 2012.
Admin system don't know how create the disks and define the raid.
The server has 12 disks (300GB). It's necessary to have disk RAID 1+0 for tempdb and transactional logs and raid 5 for data.
Which number of disks for raid 1+0 and for raid 5.


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Dr. KlahnPrincipal Software EngineerCommented:
You need a minimum of two disks for RAID 1+0.  A minimum of 3 for RAID 5 (4 and 5 is more common).

Thus you could create:

Two RAID 5 sets and one RAID 1+0 set.  (5 + 5 + 2).
Two RAID 5 sets and two RAID 1+2 sets.  (4 + 4 + 2 + 2)

RAID 6 would be a better choice than RAID 5 for business-critical data if the hardware supports RAID 6.

300 GB is a small drive by today's standards and the drives are probably older drives.  If so, RAID 6 would be a better choice in view of reliability (old drives and probably even-aged drives), but even a RAID 6 (x5) set would only be around 1 TB.  Carefully examine the amount of data you intend to be storing.  Remember that in fault-tolerant RAID sets some of the drives are used for error correction, not for data.

Rebuilding a RAID 5 array requires reading all data from all disks, opening a chance for a second drive failure and the loss of entire array. In August 2012, Dell posted an advisory against the use of RAID 5 in any configuration on Dell EqualLogic arrays and RAID 50 with "Class 2 7200 RPM drives of 1 TB and higher capacity" for business-critical data.
Lee W, MVPTechnology and Business Process AdvisorCommented:
I'd say it depends on how much data you have.

RAID 0+1/10 requires FOUR disks, not 2.  2 is RAID 0 OR 1.  When you're combining them, you need an even number of drives 4 or greater.

For RAID 5 you need a minimum of 3 disks. and RAID 6 requires a minimum of 4.  You should probably keep one defined as a hot spare.  SO, depending on the amount of storage you need which, since we don't know your application/data growth, we cannot tell you:

RAID 10/0+1/1+0
600 GB usable: 4 disk or
900 GB usable: 6 disk


Hot Spare

1800 GB usable: 7 disk RAID 5 or
1500 GB usable: 7 disk RAID 6 or
1200 GB usable: 5 disk RAID 5 or
900 GB usable: 5 disk RAID 6
bibi92Author Commented:
There is 1,5TB data.

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Scott PletcherSenior DBACommented:
I ha[v]e to setup 2 ms sql server instances on a windows server 2012.
You need two separate instances?  You don't have enough drives for that.
RAID10 = 4 drives
RAID5 = 3+ drives
= minimum of 7 drives.
Thus, for two instances, a minimum of 14 drives.
Gerald ConnollyCommented:
Just to add a thought

RAID-5 is no longer recommended for business use, due to the long reconstruct time with the current generation of extremely large disks 1TB and up.

In this case 300GB would be OK, but future requirements need to be considered also
Lee W, MVPTechnology and Business Process AdvisorCommented:
If there's 1.5 TB of data, then I would say the server storage likely wasn't sized properly.  There's virtually no room for growth EXCEPT with the RAID 5 7 disk config - and then you only have 20% growth space which seems VERY small unless your data isn't expected to grow and JUST be altered/referenced.

I haven't heard anyone before say RAID 5 was no longer recommended for business - I'd like to see WHO is saying that or if it's just your opinion.  (Rebuild times COULD be very long... and I can accept your argument that you wouldn't recommend it, but I'm not sure I'd buy that the "IT world" (not that you said that) no longer recommends.
bibi92Author Commented:
Ok so for two instances, RAID 1+0 is not possible with 12Disks 300GB.
Is it possible to have RAID 6?

Gerald ConnollyCommented:
@bibi92, of course RAID10 is possible with 12 x disks, but will only give you 6 x capacity, ie 1.8TB useable.

Incidentally the term "RAID 1+0" is ambiguous, I assume you mean "mirror sets" that are then "striped", if so MOST people ( except) Dell, understand this to be "striped mirror sets"
Gerald ConnollyCommented:
@lee - re RAID-5, you just need to look at replies from lots of experts on here, not just me, and the consensus is that because of the size of modern disks and the subsequent increase in re-build times incurred, that the risk of a second disk failure during a RAID-5 rebuild is unacceptably high.
That is why RAID-5 is not recommended for business use any more. Go either RAID10 or RAID-6
bibi92Author Commented:
If I use Raid 6, which size is useable ? Thanks
Gerald ConnollyCommented:
Raid-6 with 12x300GB drives would be 10+2 which is 3TB useable

Some might say a 12 disk RAIDset is too big and that it should be 2 x 4+2 which would give 2x1.2TB = 2.4TB
bibi92Author Commented:
Can you give me more details about your answer, please?
Gerald ConnollyCommented:
RAID-6 uses two parity disks, so with 12 disks that's 10 Data + 2 Parity ( so RAID-6 10+2)

The problem with using a 12 disk RAIDset is the rebuild time, as a rebuild means the RAID controller has for each block to read all the remaining 11 disks to generate the missing data which can then be written to the replacement disk. This 12 IOP overhead will have a big affect on performance. That's why some would recommend splitting the disks into two sets of 6 ( 4+2) which will reduce the capacity but means a disk failure will not have such a big affect on the whole system.

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Windows Server 2012

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