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Does ESXi server power down physical hard disks in ESXi server when no disk activity is detected? Or, when very little disk activity is happening it might get cached instead of spinning up the hard drive for a small write?

If the answer is yes, how can this behavior be controlled/configured ?

As a side note, I know that there is a way (officially unsupported) to attach physical disks to Guest operating systems as a RAW disk rather than a virtual disk. I wonder if the Guest operating system would then have any direct control over powering down the physical disk based on the Guest operating system's power management settings.

  • Reason for asking:

I was toying with the idea of using a spare hard drive as an additional backup target. Since that hard drive would only ever see activity when there is a backup job running, the rest of the time there would be no activity. I wondered if ESXi or a Guest OS (via raw disk, see above) could power it down to save power and wear and tear on the disk.

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  • It depends on your power settings.
    – Zapto
    Feb 7, 2013 at 17:59
  • Just as an aside: If the disk is in the same physical machine that it's backing stuff up on, it's not really a backup.
    – MDMarra
    Feb 7, 2013 at 18:09
  • @MDMarra I suppose think of it more like it's duplicating selected subset of information from one or more other physical disks. I know this is not really a back up in the traditional sense, but just humor me here :)
    – 7wp
    Feb 7, 2013 at 18:11
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    The only significant source of "wear and tear" on modern disks is from heat cycles, from turning the disk on and off. Letting the disk sit on or off constantly is significantly better for the drive than cycling. Also, if you're thinking about power usage, the amount of money you'd save from electricity would likely be less than the portion of the drive's cost assigned to the reduction in life (eg saving $50 in electricity by cutting a $200 drive's life in half would be a net loss of $50).
    – Chris S
    Feb 7, 2013 at 18:15
  • @ChrisS Then I guess there is no point worrying about power cycling. Still very informative.
    – 7wp
    Feb 7, 2013 at 18:17

2 Answers 2

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No, it does not. In most environments this also would not make any sense since

  1. there hardly ever is idle time for a hard disk hosting a data store for a number of virtual machines
  2. no RAID controller would support spinning down individual disks and running ESXi without a RAID controller with BBWC would result poor I/O performance for the guests
  3. spinning hard disks down and up is regarded as "not a thing to do" with server hard disk drives as a disk has a limited number of "load/unload cycles" which it is able to take and also might fail on a spinup due to the increased electrical and mechanical load at this time

If you need spindowns, your only option would be to separate the disk(s) out to a different enclosure where you have the appropriate level of control (e.g. to a Linux- or BSD-based iSCSI target) and reference it from either ESXi to create a data store or directly from within your guest.

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  • Thanks, of course that makes sense. I have added additional information to my question to better explain the context of my question.
    – 7wp
    Feb 7, 2013 at 18:09
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That would be a function of the server hardware, disks and array controller you're using.

By default, no, ESXi wouldn't do this, because that's an undesirable feature. Most server-class hardware wouldn't be set to spin down drives either by default.

Edit:

Something like an external USB drive, however, may spin-down. But that's a unique case.

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  • I don't know which answer to accept. both @syneticon-dj and your answers are great.
    – 7wp
    Feb 7, 2013 at 18:26

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