We know that higher temperature disks, perform less efficiently. In my DIY ZFS storage case, hdadm showed that there was insufficient cooling or air was not being moved efficiently through the cage as the temperature of the 15K rpm drives continuously inched towards the clip or shutdown temperature. The clip temperature can be seen in the output of:
smartctl -d scsi -a /dev/rdsk/cXtXdXsXRe-orientation of the drives and re-positioning a 20MM fan seems to be holding at 53 degree C. I'll focus on getting temperatures down to the 36-40 degree C range. For more use see hdadm which is a wrapper script for calling the hd binary.
... excerpt
Device supports SMART and is Enabled
Temperature Warning Enabled
SMART Health Status: OK
Current Drive Temperature: 48 C
Drive Trip Temperature: 65 C
Manufactured in week 31 of year 2006
hdadm displayA hard drive performance test can be run using:
Device Serial Vendor Model Rev Temperature
------ ------ ------ ----- ---- -----------
c0t1d0p0 DNL3P68018NM FUJITSU MAX3036NC 5D03 53 C (127 F)
c0t2d0p0 DNL3P6400SDR FUJITSU MAX3036NC 5D03 58 C (136 F)
c0t3d0p0 DNL3P68018NN FUJITSU MAX3036NC 5D03 54 C (129 F)
c1t1d0p0 DNL3P6400SEE FUJITSU MAX3036NC 5D03 49 C (120 F)
c1t2d0p0 DNL3P68018BC FUJITSU MAX3036NC 5D03 51 C (123 F)
c1t3d0p0 DNL3P68018NV FUJITSU MAX3036NC 5D03 46 C (114 F)
c2d0p0 HNCF128MMG=STCB21M84025C03356C1 MG 84025C03356C1 - None
hdadm diskqual