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I have a machine with a zfs pool on three magnetic drives /dev/sda, /dev/sdb, /dev/sdd containing larger data and a SSD with ext4 on /dev/sdc containing the rest of system (including home directories, logs, ...). I set up power saving for the drives using hdparm -S 240 to spin down after 20 minutes, but after about 8 hours of inactivity the drives sleep like this:

# hdparm -C /dev/sd[abd]

/dev/sda:
 drive state is:  active/idle

/dev/sdb:
 drive state is:  standby

/dev/sdd:
 drive state is:  standby

Does anyone have an idea why can this happen? I was thinking that all access in zfs pool would be more or less uniform over the drives in pool. How can I diagnose the cause of this problem?

Edit: I've tried enabling block dump (echo 1 > /proc/sys/vm/block_dump) for an hour and then looking into the log file. There was no access to any drive in the pool, but sda is still not in standby.

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    Is sda a different brand / firmware version that the others? Maybe it's a drive issue?
    – mpy
    Commented Feb 14, 2015 at 19:36
  • That seems to be it, thanks! smartctl tells me firmware version for sdc and sdd, but not for sda. There are the same model, but bought separately. Maybe you could make that into an answer so that I have something to accept? :-)
    – cube
    Commented Feb 17, 2015 at 8:10
  • I've written an answer. But please accept it only if you are able to solve your problem with these clues. And if so, please tell us...
    – mpy
    Commented Feb 17, 2015 at 19:55
  • The problem disappeared. Probably it just needed a reboot.
    – cube
    Commented Mar 4, 2015 at 12:47

1 Answer 1

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Here are some clues to check:

  • Is the HDD sda different from sdb and sdd in respect to brand, model or even firmware? Compare the output of hdparm -I /dev/sda etc.
  • Is sda connected to a different SATA/SAS controller?
  • Is it possible to set sda into the standby / sleeping state manually via hdparm -y /dev/sda resp. hdparm -Y /dev/sda?
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