On Fri, Sep 28, 2012 at 11:02:40AM +0800, Robin Dong wrote: > From: Robin Dong <sanbai@xxxxxxxxxx> > > Using mkfs.btrfs like: > > mkfs.btrfs -b 1048576 /dev/sda > > will report error: > > mkfs.btrfs: volumes.c:796: btrfs_alloc_chunk: Assertion `!(ret)' failed. > Aborted > > because the length of dev_extent is 4MB. > > But if we use mkfs.btrfs with 8MB total bytes, the newly mounted btrfs filesystem > would not contain even one empty file. So 12MB will be good min-value for block_count. I'm not able to create a single file even on a 12MB filesystem (with -d single -m single --mixed), so any limit that would let the mkfs finish normally should be fine. For the single/single case it's 5MB but for the dup/dup it's 156MB. It's due to the known bug in the blockgroup creation with multiple devices (applies on dup as well here) that leads to: # btrfs fi df . System, DUP: total=8.00MB, used=4.00KB System: total=4.00MB, used=0.00 Data+Metadata, DUP: total=64.00MB, used=24.00KB Data+Metadata: total=8.00MB, used=0.00 8*2 + 4 + 64*2 + 8 = 156 so, 12M is too small to avoid the mkfs crash. david -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
