>>> [root@localhost tmp]# df >>> Filesystem 1K-blocks Used Available Use% Mounted on >>> /dev/sda3 3746816 3193172 1564 100% /mnt/sysimage >>> /dev/sda1 495844 31509 438735 7% >>> /mnt/sysimage/boot >>> /dev/sda3 3746816 3193172 1564 100% >>> /mnt/sysimage/home >>> >>> So there's 1.5M of free space left according to conventional df. However: >>> >>> [root@localhost tmp]# btrfs fi show >>> Label: 'fedora_f18v' uuid: 0c9b2b62-5ec1-4610-ab2f-9f00c909428a >>> Total devices 1 FS bytes used 2.87GB >>> devid 1 size 3.57GB used 3.57GB path /dev/sda3 >>> >>> [root@localhost tmp]# btrfs fi df /mnt/sysimage >>> Data: total=2.69GB, used=2.69GB >>> System, DUP: total=8.00MB, used=4.00KB >>> System: total=4.00MB, used=0.00 >>> Metadata, DUP: total=438.94MB, used=183.36MB >>> Metadata: total=8.00MB, used=0.00
> So if I assume 2.7GiB for data, and add up the left side of fi df I get > 3224MB rounded up, which is neither 3.57GB or 3.57GiB. I'm missing 346MB at > least. That is what I should have said from the outset. 2.69 + (438.94 / 1000 *2) + (8.0 / 1000 / 1000 *2) + (4.0 / 1000 / 1000) + (8.0 / 1000 / 1000 *2) 3.567916 Looks like 3.57GB to me :p > So is the Metadta DUP Total 438.94MB allocated value actually twice that, but > only 438.94MB is displayed because that's what's available (since the > metadata is duplicated)? The capacity of the metadata group is 438.94; the actual size on disk is twice that. >> Note that the -M option to mkfs.btrfs is intended for this use-case: >> filesystems where the size of a block allocation is large compared to >> the size of the filesystem. It should let you squeeze out most of the >> rest of that 400MB (200MB, DUP). > > Is there a simple rule of thumb an installer could use to know when to use > -M? I know mkfs.btrfs will do this for smaller filesystems than this. I'm > thinking this is a testing edge case that a desktop installer shouldn't be > concerned about, but rather should just gracefully fail from, or better yet, > insist on a larger install destination than this in particular when Btrfs. I tend to go with "any filesystem smaller than 32GB", but a more accurate rule is probably along the lines of "any filesystem that you expect to normally run within half a gb of full". -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
