RAID Configuration best prwctice on HP DL360 G7 Server

I’m building a SQL 2008 Server on a HP DL 360 G7 server with five 300GB SAS drives.  It has capacity for 3 more drives.

What best practice in terms of RAID configuration from the start?

I will have logical drives as follows:

1 for OS
1 for Database
1 for Logs.

Wold I be advised to have one array @ RAID 5 for all?  Or split the OS onto another array.
DHPBilcareAsked:
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strivoliConnect With a Mentor Commented:
Since you have 5 HDDs of 300GB with an option for further 3, consider that your solutions are:

RAID1: add a 6th drive and you can create 3 Arrays of 300GB each. Each Array can have only 1 HDD failed.
RAID10: add a 6th drive and you can create 1 Array of 900GB (same space as previous scenario but much more flexible). It is built linking 3 pairs of RAID1. You can have only 1 HDD failed for each pair.

RAID1 for OS: use 2 HDDs and get 300GB.
RAID5 for Data: use the remaining 3 HDDs and get 600GB. OR...
RAID10 for Data: add a 6th HDD and you can get a 600GB Array.

The choice should be done based on many factors but the most used are:
a. Space needed,
b. Disk I/O expected,
c. Reliability. I've used tens of Arrays and the most secure, in my opinion, is RAID6.
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strivoliCommented:
I would use 1 RAID6 + 1 spare. RAID6 uses 2 disks for parity and is more reliable than RAID5. With RAID6 and 1 HDD as spare you "loose" 3 HDDs. As a result you obtain "only" 600GB. I would buy 3 more HDDs in order to have more room and increase performance.
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MaheshArchitectCommented:
You can have 2 drivers in raid -1 (Mirrioring) - keep reserved for OS
For rest of the drives, you can configure raid-5 - keep Database and Logs
If you want to add more 3 drives then you will have option of Raid-6 as well.
The difference between Raid-5 and Raid-6 is as below.
Raid-5 have one parity disk (sustain failure of 1 disk)
Raid-6 have dual parity (Sustain failure of 2 Disk)
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DHPBilcareAuthor Commented:
I have to build the server today thus can add more drives to a RAID 6 after its created?

Whats the min number of drives for RAID 6?
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MaheshArchitectCommented:
Four
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DHPBilcareAuthor Commented:
How does one array, all drives @ RAID 6.

Should give me 900GB usable.

Is it wise to include Windows, Data and logs in the same array?
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DHPBilcareAuthor Commented:
I'm happy being able to stay up with a two disk failure.
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strivoliCommented:
You can add more drives to a RAID 6 depending on the RAID CTRL itself. Usually it allows expanding a RAID Array.
RAID6 requires a minimum of 4 HDDs.
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strivoliCommented:
Yes you'll get 900GB.
Win/Data/Logs in the same Array? If you had several disks (10 or more) I would have created more Arrays but in your scenario 1 Array is the only solution. I don't see any problems with a single Array.
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Miguel Angel Perez MuñozCommented:
RAID configuration must depends of I/O of database. Remember RAID 5 have poor performance on write operations (because needs calculate parity and write on disk) and lot of little transactions on disk causes performance may be rubbish.

RAID 1/RAID 10 may offer better write performance to databases and better fault tolerance.
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Handy HolderSaggar maker's bottom knockerCommented:
RAID 6 write performance is even worse than RAID 5 write performance plus you need the Smart Array Advanced Pack licence to use it. I'd use RAID 1 for the OS and unless the DB is very write intensive I'd put the transaction log volume on that pair of disks too, then use RAID 5 or 10 for the data.

You can change RAID levels on the fly assuming there is enough space that's not taken up with logical drives but that requires battery/flash backed write cache.
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