tempdb on raid1 isolated or raid10 shared with high write db
I found these articles helpful:


Why RAID10 (0+1) superiority is a myth (specifically versus RAID1).
And this is an additional guide on raid level comparison.


Further reading suggests that the benefits of using RAID1 for log files (assuming isolated from data files) is lost when more than 1 log file exists on that RAID1 array. This is due to the sequential nature of the transaction log writes to disk. The sequential write benefit is lost when multiple log files are accesses on the same RAID1 array due to the random nature of access on a spinning disk. This would suggest that RAID10 is the better choice in a multiple DB environment unless you have the disks to isolate each log file.

These stats below sold me on proposal 3, isolating tempDB on RAID1 by stealing 2 disks from LOG array moving log array from RAID10 to RAID1.  Basing much of this on RAID1s ability to maintain good WRITE speed.

TEMPDB is clearly under more stress than I have realised.

These table rankings ring true for snapshot values during normal operation (not just the accumulated totals) as we do have intensive out of hour routines.

TOTAL IO:

db.tempdb.mdf = 144,747,290,352

db.2.mdf =         100,482,243,080

db.2.ldf =           2,571,065,773

db.s.mdf =         1,702,508,040

db.s.ldf =           223,032,162

TOTAL READS:

DB.2.mdf =         84,851,614,280.00

db.tempdb.mdf = 72,271,813,552.00

db.s.mdf =         1,691,504,864.00

db.2.LDF=          93,822,304.00

TOTAL WRITES:

db.tempdb.mdf = 72,475,476,800

db.2.mdf =         15,630,628,800

db.2.ldf =           2,477,243,469

db.tempdb.ldf =   222,946,079


One possible concern maybe the additional of the tempdb ldf and mdf on the same raid1 array but if this is a problem tempdb.ldf can be moved to the log array.

These are helpful links that explain TEMPDB usage, what it does and how it may effect my apps:


http://bradmcgehee.com/wp-content/uploads/presentations/Optimizing%20tempdb%20Performance_SQLCONN.pdf
http://blogs.msdn.com/b/cindygross/archive/2009/11/20/compilation-of-sql-server-tempdb-io-best-practices.aspx