Re: UFS2 optimization for many small files

On 2007-Jun-27 14:11:19 +0400, Nguyen Tam Chinh <unixvn@xxxxxxxxx> wrote:
We're going to build a server with some 1Tb of over 500 million small
files with size from 0,5k to 4k. I'm wonder if the ufs2 can handle
this kind of system well.

Short answer: No.

Longer answer: FreeBSD and UFS2 have been tweaked to support large
numbers of files in larger filesystems and there are no hard limits
that you will exceed by having 500,000,000 files in a >1TB FS.

However, you will not be able to fsck the FS on an i386 system and
will need a lot of RAM+SWAP on amd64 or SPARC64. fsck will also take
a _long_ time (hours) to run. Depending on how the files are organised,
you may run into severe performance problems with directory searching.

From newfs(8) the min block size is 4k. This
is not optimal in our case, a 1k or 0,5k block is more effective IMHO.
I'd be happy if anyone can suggest what does fragment (block/8) in the
ufs2 mean and how this parameter works.

I suggest you read /usr/share/doc/smm/05.fastfs/paper.ascii.gz
Whilst this paper discusses UFS1, the basics remain the same.

I have tried using a 4K/0.5K UFS1 filesystem in the past and found the
performance was very poor. UFS2 was based on 16K/2K and I would expect
it to perform even worse with 4K/0.5K. I would suggest you try 8K/1K.

BTW, in sizing your system, you will need to allow for both the last
space when the file sizes are rounded up to a multiple of the fragment
size, as well as the inode size (256 bytes). If you have 1TB of data,
it's likely that you will have another 0.5-1TB of overheads.

Overall, I suggest you look at an alternative way to store the data.

--
Peter Jeremy

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