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I have a Ubuntu file server and it makes the oddest sound. I can hear a HD making a "breathing" type sound, like the disc spins up for a moment and then cycles down. It happens on a very regular basis, about every 20 seconds or so. I've run every HD diagnostic I can think of, and I can't figure out what might be causing it.

The system runs Ubuntu 11.04, with a OS HD & 4 discs configured in a RAID5 array.

Is this something I should be worried about? Is there any utility I can run to see why the disc keeps spinning up?

EDIT: Here's a link to a sound recording of the sound.

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As a precaution, get a full backup as soon as possible before investigating the drives any further. Then, look into power management and related settings. After that, make sure your power supply isn't starting to fail. – Randolf Richardson Aug 15 '11 at 21:40
Oh, and you might also want to check for prank software that periodically plays breathing sounds from your sound card. ;-D – Randolf Richardson Aug 15 '11 at 21:42
could you get a recording of said sound? – Journeyman Geek Aug 15 '11 at 23:38
Early days of SkyNet becoming "self aware" – Nick Josevski Aug 16 '11 at 0:05
Remember run SMART tests periodically in all disks. – Rufo El Magufo Aug 18 '11 at 18:00

My theory is that you have multiple disks (or fans) that are generating (pseudo) white noise slightly out of phase. When they are in sync the cumulative noise is either amplified or canceled out, and as they oscillates between phases the cumulative noise increases & decreases. This would cause a cycle of louder and quiter periods of while noise, which could sound like breathing.

To test this theory, you would need to spin down each disk (or fan) one by one to determine where the noise is comming from. If spinning down any one of the disks stops the noise (or any one in a subset of disks, as not all disks may be contributing to the noise), then my theory is correct.

If this theory is correct, then the noise is harmless.

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How would I spin down each disc, including the discs in the raid? – jonnyflash Aug 18 '11 at 17:03
hdparm -y /dev/sdx (change sdx appropriately). Note that accessing that disk will immediately spin it back up, so try to prevent disk access while testing. I don't know how you're RAID is configured, so I don't know if you have that control for those disks. You may need to use RAID tools to take an individual disk offline. – Klox Aug 19 '11 at 4:18

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