striping across multiple AutoRAID

[Mark Bak]

If I have 3 12H AutoRAIDs, (running Baan & Oracle, the database is about 100GB ) would it provide better performance to stripe LUNs across the AutoRAID, or create multiple LUNs on each AutoRAID and alternate putting the most accessed/busy files on a different AutoRAID?

[Bob Inglis]

The best performance would probably be acheived by creating 2 or more LUNs per AutoRAID and striping accross all LUNs taking care to use both hardware paths (X and Y controlers)

[A. Clay Stephenson]

Hi Ron,

The highest performance no doubt would be achieved by splitting the I/O across all 3 12H with each volume group defined as 2 logical volumes of equal size and striped so that LUN0's primary path is thru controller X (alternate Y) and LUN1's primary path is thru controller Y (alternate X). Also, leave as much space unallocated as possible so that the 12H's stay in RAID 01. You then strip each logical volume across both LUNS.

I've found that I get the best performance on vxfs filesystem logical volume with striping set to 64K. Mount your data and index files
with vxfs options convosync=direct,mincache=direct,nodatainlog.

This will bypass the unix buffers and give you the benefits of raw io.

Mount the archive & redo logs, and baan data with the typical vxfs options (nodatainlog).

Regards, Clay

[Mark van Hassel]

Hi Ron,

I agree on using all 3 autoraids and alternating X and Y controllers as primary and alternate path. According to the manuals its best (performance wise) to confgigure about 4 or 5 luns per autoraid (be aware that 8 is the maximum !). I do not agree that striping will increase performance since you do not know on which physical disks the autoraid will put your data and the gain by alternating the primary paths can be reached by creating more than 1 LUN.

The mincache=direct option in vxfs is only available when Advanced JFS is installed I believe.

Good Luck,
Mark.

[A. Clay Stephenson]

Hi again,

There is no benefit to going beyond 2 LUN's on a single AutoRAID unless more than one host is connected. The reason you stripe lvols is so that both EXTERNAL buses are fully utilized. On an AutoRAID striping across disks has no meaning, we are simply forcing writes to the same lvol to be split across both paths.

If you attempt to balance external bus loads by creating more LUN's you may succeed. By striping across 2 LUN's you always succeed.


Regards, Clay