I am looking to create a second raid6 set which will only be used to do periodical backups of the main raid6, probably using rsync. (all drives will be tler'able WD reds) Obviously when the system boots all the raids will start up, but I am looking to run some kind of script that will force the drives into a "hard sleep" for want of a better term. At the moment none of the drives have any sleep or power down timers set, in part to fix the idle3 bug increasing the load cycles count and this will be applied to the new drives as well. My questions are: 1) I am using EXT4, will I need to "do something" to make sure that it flushes all changes to disk (which I assume means "flush to MD layer"), if so what? 2) Likewise with the MD layer, is there any command that forces it to flush to disk any cached changes? 3) I am guessing that I need to issue a hdparm to each disk in the raid set to send it either to sleep or spin down or some such state, as the backup raid will not be accessed except during backup writes or data recovery it can go into the most "asleep" state available. 2 questions, what hdparm setting? also is there a smartctl equivalent? 4) As the drives might take a length of time to waken, does this need to be considered by the /sys/class/scsi_device/*/device/timeout value to prevent that layer deciding the disk has gone walkabout if it takes to long to wake up? 5) If there isn't any easy way to make sure the raid/file system has flushed any changes would a reasonable method be to unmount the file system, then stop the raid, then send the drives to sleep? 6) Obviously if this (5) is the only way or best way I am guessing the backup script would just need to assemble the array to start it (--scan --assemble --uuid=) which should wake up the drives and then mount the file system, then call the script that performs the unmount,stop,sleep? 7) does sending a drive "to sleep" make sure that everything in the drive cache is sent to disk? 8) I am using debian jessie, and the smartd checks for changes in smart values (temp is the one that is listed most, almost exclusively, in /var/log/syslog) will this cause my drives to wake up or is it clever enough to see the drive is sleeping so won't wake it? Finally, does anyone else do something similar or do most users either just leave the backup array running, which seems a bit of a waste both in power and drive lifespan terms especially if backups are fairly infrequent (this won't be daily, probably weekly or monthly at most, so not having to sleep/wake drives on a daily basis putting a different type of wear on them)? Jon -- 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
