Re: Allocation strategy - dynamic zone for small files

[Andreas Dilger <adilger@clusterfs.com>]

On Nov 14, 2006  00:32 +0100, Ihar `Philips` Filipau wrote:
> As person throwing in the idea, I feel bit responsible. So here go my
> results from my primitive script (bear with my bashism) on my plain
> Debian/unstable with 123k files on 10GB partition with ext3, default
> 8K block.
> 
> Script to count small files:
> -+-
> #!/bin/bash
> find / -xdev 2>/dev/null | wc -l
> find / -xdev -\( $(seq -f '-size %gc -o' 1 63) -false -\) 2>/dev/null | wc 
> -l
> find / -xdev -\( $(seq -f '-size %gc -o' 64 128) -false -\) 2>/dev/null | 
> wc -l
> -+-
> First line to find all files on root fs, second to find all files with
> sizes 1-63 bytes, third - 64-128. (Param '-xdev' tells find to remain
> on same fs to exclude proc/sys/tmp and so on)
> 
> And on my system counts are:
> -+-
> 107313
> 8302
> 2618
> -+-
> 
> This is 10.1% of all files - are small files under 128 bytes. (7.7% < 63 
> bytes)
> 
> [ Results for /etc: 1712, 666, 143 (+ 221 file of size in range
> 129-512 bytes) - small files are better half of whole /etc. ]

Note that using the root filesystem is a skewed result (esp. on GTK systems
where lots of single-valued files are used by gconf).  Many root filesystems
using ext3 are formatted with 1kB blocks for this reason.  Also gather stats
for other filesystems.

At the filesystem summit we DID find a surprising number of small files
even when the whole system was examined.  We discussed storing small
files directly in the inode along with other EAs (this would require
larger inodes).  This improves data locality and performance (i.e. stat
of the file loads the small file data into cache), though the assumption
is that there will be an increasing number of EAs on files in the future.
It also avoids the issues w.r.t. packing file data from different files
into the same block and they have different lifespans, etc.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.