Are there any ideas why one backup drive is outperforming the other by such a wide margin?
I routinely use two 1TB hard drives to store Time Machine backups. One is an internal Hitachi 1TB hard drive I bought from Apple and the other is a 1TB OWC Mercury Elite 1TB external FW800 hard drive from OWC. My main hard drive is a 1TB Hitachi internal drive that I bought from OWC. During the day, I change the backup destination drive by using the Select Disk option on TM preferences. At the end of the day, both backup disks have up-to-the-minute TM backups.
Over time, I noticed that the number of days between the oldest TM backup and the date of observation was much larger for the internal Hitachi from Apple. I then recorded 10 observations between April 7, 2010 to May 4, 2010. During that time, the OWC external drive's number of days varied from 2 to 9 days (average 5.9 days) while the internal Hitachi drive's number of days varied from 11 to 25 days (average 17.8 days). The average number of days for the internal Hitachi were 3 times more than for the OWC external drive.
Disk Utility shows that both backup drives have the same capacity. The OWC drive's used space varies from 595GB to 922GB but for the other 8 observations, it was in the mid 700 to upper 800 GB range. The internal Hitachi's used space was consistently in the low 900GB range.
Other info that may be useful: The main hard drive routinely has used space of 270GB, plus or minus a few GBs depending on what has been added and deleted. The largest item to be backed up is a VMware virtual machine that contains Windows 7 Ultimate. It weighs in at 160GB including all Windows apps & data (that's 59% of the main hard drive's used space).
Any suggestion as to how I can improve the performance of the OWC Mercury Elite?
