topic Re: EVA used sapce in Disk Enclosures

EVA used sapce

Martin Hodgson — Wed, 04 Feb 2009 15:25:17 GMT

Hi,
Is there a way of understanding how much space is actually being used on a vdisk as opposed to allocated? I know I could go to the server and try and work this figure out but just wondered if there was a trick to working that out from the EVA perspective.

Thanks in advance,
Mike

Re: EVA used sapce

Víctor Cespón — Wed, 04 Feb 2009 15:32:20 GMT

The usage is a filesystem question, the EVA does not know about filesystems, it just uses data blocks.
As you write and delete files, most blocks will have some data on it, even if it belongs to a deleted file, the EVA does not know that.
The EVA does not read the MFT, or whatever table the OS uses to keep track of which files are active and which are deleted.

Re: EVA used sapce

Martin Hodgson — Wed, 04 Feb 2009 16:04:40 GMT

Closed

Re: EVA used sapce

Uwe Zessin — Wed, 04 Feb 2009 17:54:53 GMT

Some storage arrays _do_track the _block_ ranges which have been written at least once and the management tool can show a graphical representation - I've seen it on the HP VA7000 series.

As far as I can tell, the EVA (which shares no development history with the VA7000) does track it, too, in order to optimize CA + BC replication (never-written areas do not get 'copied'), but this information is not accessible (at least by the end-user).

Re: EVA used sapce

Víctor Cespón — Wed, 04 Feb 2009 21:05:58 GMT

Yes, the EVA knows what blocks have been modified, but as I explained above, when the OS deletes a file, it does not touch the blocks that from the file, only the FAT or MFT, so for the EVA those blocks contain data. So no correlation between what blocks the EVA sees as used and what what the OS sees as used.