APMtimer provides a Linux/Unix utility that can permanently Disable, Get, or Set the value of the APM timer found in recent Western Digital 2.5 WD*PVX Hard Disks where the APM setting defaults to 0x60 after a power cycle.
Thank you for this tool, i was an unhappy owner of a WD2500LPVT-00G33T0 drive which was quiet but had the dreaded WD idle spindown "feature" after like 5 seconds. Setting the APM to 255 from the default 92 did fix it, but it was a fix that had to be redone after every power cycle. I believe i had tried WDidle along with idle3-tools with no success. I found this tool and at first i had little hope since it reported the idle timer to be 0xc800 (20s), but i tried disabling it anyway and it WORKED! The drive does not spin down anymore, even after a power cycle. No need to change the APM value either. I can finally put it in an usb enclosure and finish my Pi torrent box, without the drive killing itself slowly.