I recently bought a couple Western Digital 1.5TB "Green" Drives (WD15EADS) to rebuild my home media storage array with higher-density disks. I already had one Segate 1.5TB drive (ST31500341AS) I was using for a "scratch" drive (rpm mock builds, storing MythTV recordings, secondary backup) that I had problems using at all until Seagate released a firmware update, so I was skeptical about buying more of those. I thought the green drives would be fine; that despite their variable rotational speed, the power savings and ability to spin up to higher speeds when needed would work out fine.
Unfortunately once I had a couple of these drives in a software RAID 5 array I began to notice problems. When copying data to the array I would see decent transfer rates of ~33MB/s for 30-40 seconds but I would then see the transfer rate drop to 200-500KB/s for 2-3 minutes. Since the array was initially built with only the WD drives I was pretty sure the problem was isolated to those drives. Even after adding the Seagate drive the problems remained.
To test my assumption that the WD drives were somehow causing problems I began an rsync and waited until the transfer "paused". I then did a "dd" against each of the drives in the array, seeking to a new position in the drive between tries. It consistently showed the WD drive only getting 100-250KB/s while the Seagate drive would get ~90MB/s.
Once replacing all the WD drives with equivalent Seagate drives the array is resyncing at ~90MB/s; almost 3 times what I was getting with the WD drives alone.
When I first started seeing these problems with the WD drives I thought it might be related to the idle command so I downloaded the WDIDLE3.exe program to increase the idle time from the default 8 seconds to 25 seconds, and then later disabling the idle time out. When this didn't fix anything I downloaded the WDTLER.exe program to enable TLER for the drives which also didn't affect the drives at all (I didn't expect this to since I wasn't seeing data completely stop or the drives drop out of the array).
I'm not sure what to do with these WD drives; while they seem to work fine independantly, they don't perform correctly at all when put into a RAID array. I'm beginning to get afraid that as the hard drives get larger and larger the complexity of the firmware is growing too quickly for drive manufacterers to keep them performing reliably.