Is spooling down normal for a SCSI HDD?

I have a few SCSI HDDs I'm playing around with for the first time - they weren't any cost to me, so I thought I would experiment with them. Is it normal for a SCSI HDD to randomly (seemningly random) spool down? Er, or it seems to be winding down for no reason. In Windows Vista, when I view Computer --> Computer Management --> Disk Management, I note the drive in question is no longer "Active". When I "Mark Partition as Active" it spools up again no problem. They work nicely otherwise. Is there a problem with the HDD or is this normal for SCSI devices?

Windows Vista Premium 32bit
Intel Core 2 Duo E6600 @ 2.70GHz
BFG GeForce 8800 GTX OC
Corsair XMS2 TWIN2X2048-6400 2X1GB DDR2-800
Western Digital 150GB Raptor x2 RAID 0 - OS
Western Digital 150GB Raptor - Data
Seagate Cheetah 18GB 15k - Swap
IBM Ultrastar 40GB 15k - Backup
Sound Blaster X-Fi XtremeGamer Fatal1ty Pro Series
Dell E207WFP & Samsung SyncMaster 213T
Asus Striker Extreme Motherboard
PC Power & Cooling Turbo-Cool 1KW-SR
Zalman CNPS9700 NT CPU cooler
Silverstone Temjim TJ07
Pioneer DVR-212D DVD/CD Writer
APC Back-UPS XS 1000
Coolit Beverage Chiller (pride of the system)
Various trick lighting and LEDs