On Tue, Nov 18, 2014 at 02:39:48AM -0800, Robert White wrote: > Howdy, > > How does one get the exact size (in blocks preferably, but bytes > okay) of the filesystem inside a partition? I know how to get the > partition size, but that's not useful when shrinking a partition... > > So, for example, you successfully do > > btrfs filesystem resize -32G /dev/sdz2 > > now you've got "some space" zero idea how many sectors can be > trimmed off the end of the partition, you can do the math but thats > a little iffy, especially if the file system didn't originally fill > the partition to begin with. > > The current methodology for most such actions is to way over-trim > the file system, then reallocate the space using your partition tool > of choice, then re-grow the filesystem to fit. This has been the way > of things forever and it blows... > > There needs to be an option to btrfs filesystem show that will tell > you XXXXXblocks, not Y.ZZ terabytes.
The 3.17 userspace tools should now support flags to select the display units in some detail, including bytes. Even without that, though, for your use case, I would recommend shrinking the FS by *more* than you wanted to shrink, resizing the partition, and then resizing the FS back up to fit the partition exactly (with btrfs fi resize n:max). Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Stick them with the pointy end ---
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