D Cee
2 Bronze

Group manager not reporting free space

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Hi all,

I have 3 seemingly identical volumes set up and attached to the same Windows server. None of them are at capacity but in Group Manager the first 2 show up as having no free space available. The third reports the correct amount of free space as shown in Windows.

The only difference between these three volumes is that the first two were set up some time ago by another user. I set up the third recently.

Does anyone know why Group Manager might be seeing these first 2 volumes as full? I can't see any difference in the config.

Many thanks,

Don

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DELL-Donald Wi
DellEMC

Re: Group manager not reporting free space

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Hi Don,

 That's actually expected.  Currently the array is a block storage device.   You send data to it and it gets saved at the address you request.  When you delete a file, that's actually another WRITE to the array.   Free space is tracked by the OS in its File allocation table.   Something the array can't see.  So what you see on the array is a high water mark.  It will only go up.  Also, the default behavior of Windows is to do a small WRITE with every READ.   Where the last access date/time get updated on every read, for every file and directory.  Especially in virtualized environments these add up.  You can disable this in the Windows registry.

Now, with the next release of EQL Firmware we are supporting a new SCSI feature, called UNMAP.   This is actually a command sent to storage that tells the device to unallocate that block.  So in the future you will have a much more accurate representation in the GUI.  Until then only reference what the OS says for free space.   Previously allocated blocks will be re-used automatically, since again it's the OS that tracks the free LBAs.  So when the GUI goes to 100% allocated nothing need be done.  

One thing about the UNMAP command is not all OS's support it.   Currently MS has said they won't support it until Server 2012/Windows 8 is released.    Linux with EXT4 does,  ESXi v5.0 with VMFS-5 supports it, but not automatically.  You have to run a command to manually request unallocated LBAs get released.   That's expected to be fixed at a future date.

Regards,

Social Media and Community Professional
#IWork4Dell
Get Support on Twitter - @dellcarespro

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3 Replies
DELL-Donald Wi
DellEMC

Re: Group manager not reporting free space

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Hi Don,

 That's actually expected.  Currently the array is a block storage device.   You send data to it and it gets saved at the address you request.  When you delete a file, that's actually another WRITE to the array.   Free space is tracked by the OS in its File allocation table.   Something the array can't see.  So what you see on the array is a high water mark.  It will only go up.  Also, the default behavior of Windows is to do a small WRITE with every READ.   Where the last access date/time get updated on every read, for every file and directory.  Especially in virtualized environments these add up.  You can disable this in the Windows registry.

Now, with the next release of EQL Firmware we are supporting a new SCSI feature, called UNMAP.   This is actually a command sent to storage that tells the device to unallocate that block.  So in the future you will have a much more accurate representation in the GUI.  Until then only reference what the OS says for free space.   Previously allocated blocks will be re-used automatically, since again it's the OS that tracks the free LBAs.  So when the GUI goes to 100% allocated nothing need be done.  

One thing about the UNMAP command is not all OS's support it.   Currently MS has said they won't support it until Server 2012/Windows 8 is released.    Linux with EXT4 does,  ESXi v5.0 with VMFS-5 supports it, but not automatically.  You have to run a command to manually request unallocated LBAs get released.   That's expected to be fixed at a future date.

Regards,

Social Media and Community Professional
#IWork4Dell
Get Support on Twitter - @dellcarespro

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D Cee
2 Bronze

Re: Group manager not reporting free space

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Hi Don!

That's unfortunate but it makes sense. It's no big deal, I'll just make sure to rely on the OS in future.

Thanks for the help!

Don

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DELL-Donald Wi
DellEMC

Re: Group manager not reporting free space

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You are very welcome!

Social Media and Community Professional
#IWork4Dell
Get Support on Twitter - @dellcarespro

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