# ext3 poor random read performance on large filesystems

## HeissFuss

I'm seeing poor random read performance on ext3 vs XFS or ext4 for seeks at random locations in large files (20-100GB) on the filesystem.  After looking into this, it appears that it's due to inode cache misses.

Is there a way to increase inode_cache or ext3_inode_cache?  There seems to be a kernel boot tunable (ihash_entries) but no matter what I set it to, actual slab usage for inode_cache doesn't go above 3.5MB.  I'd be willing to use over 100MB for inode cache if possible.

Any ideas, or anyone know if there's a hard limit in there somewhere for inode cache?

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## x22

Have you tried lowering  /proc/sys/vm/vfs_cache_pressure (documentation here)?

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## HeissFuss

 *x22 wrote:*   

> Have you tried lowering  /proc/sys/vm/vfs_cache_pressure (documentation here)?

 

Yes, I've tried setting it to 0 or 1, but more testing indicates that the behavior is no different than for the default of 100.  It seems that there may be a hard limit somewhere related to this cache, or the cache that vfs_cache_pressure is related to is not the one I'm trying to retain (block pointer inodes.)

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