I was playing with the new hdparm wiper script ( http://sourceforge.net/projects/hdparm/files/) on my Vertex SSD and it appears that btrfs needs a huge space overhead when dealing with fallocate system calls. Basically what the wiper script does is to fallocate one huge file using all free space minus a safety margin. And this margin has to be about 30% on btrfs, e.g.:
# df -T / Filesystem Type 1K-blocks Used Available Use% Mounted on /dev/root btrfs 31266648 10464096 20802552 34% / # hdparm --fallocate 20002552 test_temp test_temp: No space left on device # hdparm --fallocate 16002552 test_temp test_temp: No space left on device # hdparm --fallocate 15002552 test_temp # and from dmesg: no space left, need 20482613248, 4096 delalloc bytes, 9786335232 bytes_used, 0 bytes_reserved, 0 bytes_pinned, 0 bytes_readonly, 0 may use 25545211904 total no space left, need 16386613248, 4096 delalloc bytes, 9786335232 bytes_used, 0 bytes_reserved, 0 bytes_pinned, 0 bytes_readonly, 0 may use 25545211904 total My question is if 30% isn't a bit too much overhead? -- Markus -- 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
