Bad performance when accessing a lot of small files

[Alexandre Biancalana]

On 12/21/07, Alfred Perlstein <alfred at freebsd.org> wrote:

Hi Alfred !

>
> There is a lot of very good tuning advice in this thread, however
> one thing to note is that having ~1 million files in a directory
> is not a very good thing to do on just about any filesystem.

I think I was not clear, I will try explain better.

This Backup Server has a /backup zfs filesystem of 4TB.

Each host that do backups to this server has a /backup/<hostname> and
/backup/<hostname>/YYYYMMDD zfs filesystems, the last contains the
backups for some day of that server.

My problem is with some hosts that have in your directory structure a
lot of small files, independent of the hierarchy.

>
> One trick that a lot of people do is hashing the directories themselves
> so that you use some kind of computation to break this huge dir into
> multiple smaller dirs.

I have the two cases, when you have a lot of files inside on directory
without any directory organization/distribution but I also have
problems with hosts that have files organized in a hierarchy like
YYYY/MM/DD/<files> having no more that 200 files in the day directory
level, but almost one million of files in total.

Just for info, I made the previous suggested tuning (raise dirhash,
maxvnodes) but this improve nothing.

Thanks for your hint!