On Sat, 21 Jan 2006, Gerd Knops wrote: > Hi, > > I have a RAID5 setup with 3 250GB SATA disks. Often the RAID is not > accessed for days, so I wonder if I can extend the life of the disks > by spinning them down, eg by setting the spindown timeout for the > drives with hdparm -S nn. > > The hdparm man page says "[after spindown] the drive may take as long > as 30 seconds to respond to a subsequent disk access". Could that > cause a timeout when accessing the disks, resulting in one or more > disks being marked bad? Hi, AIUI, It's generally safe to use spin-down. I used it for several years on a RAID-1 set with good results. However... You have N disks in a RAID-X set, and you do a sequential read, it could then takes N times the spin-up time before you can start to stream data )-: Or maybe, you get a little bit of data then a pause as the next disk spins up, then more data, then a pause, and so on. This may or may not be an issue for you though, but at between 10-20 seconds per disk could be come annoying quite quickly! The other major issue is making sure they stay spun-down once you turn them off. Using hdparm, while sounding like a good thing isn't actually that good. Too many things running on your server will keep them going - eg. ext3 likes to peek at the drives every 5 seconds (and it's probable that other journaling FS's to some extent or other). Then there's log-files - you'll need to go through syslog.conf and "-" every file to suppress the fflush. And then the kernel just wants to flush its buffers from time to time because it's in a good mood. What I used was something called noflushd. It takes care of the kernel buffer flush, by keeping it all in memory until theres no more memory. This it worked well for me with ext2 and kernel 2.4.X. The down-side of keeping all writes in memory is that if you have a power failure then things can go quite wrong quite quickly... (I UPSd that particular box) Get noflushd from: http://noflushd.sourceforge.net/ I retired that particular server after 3 years of use in a home office environment and the new one has ext3 and doesn't spin down the disks (yet!) Gordon - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
