I have written a buggy program that has accidentally created about 30M files under /tmp. (The bug was introduced some weeks ago, and it was creating a couple of subdirectories per second.) I could rename /tmp to /tmp2, and now I need to delete the files. The system is FreeBSD 10, the root filesystem is zfs.
Meanwhile one of the drives in the mirror went wrong, and I have replaced it. The drive has two 120GB SSD disks.
Here is the question: replacing the hard drive and resilvering the whole array took less than an hour. Deleting files /tmp2 is another story. I have written another program to remove the files, and it can only delete 30-70 subdirectories per second. It will take 2-4 days to delete all files.
How is it possible that resilvering the whole array takes an hour, but deleting from the disk takes 4 days? Why do I have so bad performance? 70 deletions/second seems very very bad performance.
I could delete the inode for /tmp2 manually, but that will not free up the space, right?
Could this be a problem with zfs, or the hard drives or what?
Best Answer
Deletes in ZFS are expensive. Even more so if you have deduplication enabled on the filesystem (since dereferencing deduped files is expensive). Snapshots could complicate matters too.
You may be better off deleting the
/tmpdirectory instead of the data contained within.If
/tmpis a ZFS filesystem, delete it and create again.