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Optimal Disks and Configuration for "SAS Work" space on a new W2K3 x64 SAS server

Posted on 2009-05-14
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Last Modified: 2013-11-16
I am building a new W2K3 x64 server to support SAS 9.2 64 bit edition via Citrix Presentation Server 4.5 as a Published Application, and have a question about optimal configuration for the SAS Work area. This is an HP DL380 G5 with 16 Gb RAM.  For the most part the SAS workload can be characterized as predominately large sequential IO requests with high volumes of data.

Here are the separate drive arrays I currently have envisioned:
 1) OS will be 2 mirrored 72 Gb 15K SAS disks
 2) Windows Pagefile will be a separate 36 gb 15K SAS disk
 3) SAS User Data Storage will be 200 Gb RAID5 array on iSCSI SAN
 4) "SAS Work" is temporary processing space used by the application typically for large sequential IO, and will be local 15K SAS disks on the server.  Thinking I need about 100 Gb of shared space for all users.

Here are options I've considered for this "SAS Work" temporary space:
     a) 1 x 146 Gb SAS drive at 15K (RAID0, no redundancy, if it fails I'd need to replace immediately to get server up again, but I think this would be OK in our situation of having just a few heavy users).
     b) 2 x 146 Gb SAS drives at 15K (RAID1 mirror). No real down side other than the added cost.
     c) 4 x 36 Gb SAS drives at 15K (RAID5).  Might my performance with these 4 smaller disks actually be better, even though they have the parity overhead of RAID5?

Does anyone have guidance on how to configure the disks to support this "SAS Work" in terms of picking the size, speed, number of disks, and RAID levels?  I have looked at each of the articles below, but still asking this question!

Best Practices for Configuring your I/O Subsystem for SAS®9 Applications
http://support.sas.com/rnd/papers/sgf07/sgf2007-iosubsystem.pdf 

ETL Performance Tuning Tips
http://support.sas.com/resources/papers/ETLperformance07.pdf 

How to Maintain Happy SAS®9 Users  IT focused
http://support.sas.com/resources/papers/proceedings09/310-2009.pdf
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Question by:Herrmannator
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feaglin earned 200 total points
ID: 24389992
  I'd go with the RAID 1 C: drive and have the pagefile on there, and have a RAID 10 data drive for the work space.  We just leave the page file on C: now.  With the application installed on the data partition and that much RAM there isn't much call to access OS files from the disk, so the pagefile can use the IO capacity of the mirrored C: drive.

The smaller size drive either the same speed as the larger drive, or isn't fast enough to make a difference.  From the way you describe the workload the RAID 5 might slow you down enough to make RAID 10 worth it.  If you've got the luxury of time and hardware you could do some benchmarking with the application.


hth
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by:andyalder
andyalder earned 100 total points
ID: 24395084
Have you already got the iSCSI SAN? it would be faster and probably cheaper to use a pair of internal 300GB 10Ks for that if not.
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by:Aloysius Low
Aloysius Low earned 200 total points
ID: 24409994
hi Herrmannator,

how critical is the system? how easy is it to get a replacement hard disk for a failed one?

essentially SAS work is to store temporary files generated during the session, and used for sorting among other things. if it isn't that critical or replacement hard disks are readily available, having SAS work on RAID 0 isn't a bad idea as there is really no need to replicate the data onto another hard disk for failover.

in addition, if you are going to have large volumes of I/O, having the disks on RAID 5 will probably slow things down significantly, and imagine the amount of I/O required when the data belonging to a session is cleared out...
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by:Herrmannator
ID: 31581683
Sorry I am still working with SAS and HP and testing optimal solution but appreciate your response.
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