Printed 2017/08/23 04:17AM

NTFS Allocation Unit Size

By Steve Jones, 2006/09/08

I ordered some new drives for our Dell server from "This Old Store" recently and they came on Tuesday of this week. So after delaying for a day, I got down to the colocation center Thursday and installed the drives. The folks at This Old Store had provided the right trays and so I matched up the proper SCSI drives (U160 v U320) with the proper servers and installed the drives in the servers hot.

I was slightly nervous, not wanting to have my production SQL Server crash, but it was nice to just get the drives in there and lit up. After a few minutes the DELL Array Manager picked them up, allowed me to setup the RAID 1 mirror and then format it. While I got progress data from the console, when I returned home (wait around for a format, are you kidding??!!?), I couldn't tell how far along things were. After checking once an hour for a couple hours I gave up until this morning.

So I get up today and I log into the SQL Server and see the drive there formatted by the Array Manager. Now I need to initialize it in Windows and then format it. It's a simple process in the GUI, but I get to the Allocation Unit Size and pause. Seems I've read something about this before. So I google a little and find lots of information on what it is, but not a lot on tuning this particular setting for SQL Server. Seems most of the focus is on array setting.

I did find a few notes from Neil Pike and Andrew Kelly, MVPs that said to leave it at the default. This is a W2K3 server running SQL Server that has had everything on one RAID 5 array, but I'm moving the logs to the RAID 1 array. No spare still, but since I'm not ready to rebuild this server yet and do two RAID 1 arrays, I'll leave this as is. I am tempted to do that when we move to SQL 2005, but no timeline on that yet.

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