Re: Number of ACL-Entries

On Wed, 2006-07-26 at 09:54 +0200, S. Klaiber wrote:
> Hi there,
> 
> I just joined the list and I am new to mailinglists at all. 
> 
> I intend to define up to 7000 entrys into an acl on a ext3 filesystem, Kernel 
> 2.6.9-34, which will also be accessed via NFS. I read and verified that it is 
> only possible to define up to 500 entrys. 
> 
> I tried to find out the general limit and I only got the above information 
> from a redhat mailinglist. Macro-variables like the old EXT3_ACL_MAX_ENTRIES 
> (kernel 2.4.21) which bound the limit to 32 (due to the block size) do not 
> exist anymore and I didnt find out how the limit is defined in newer kernel 
> versions yet. And I also don't know what other logical factors these limits 
> depend to. 

The acl is stored as an extended attribute (xattr), and the maximum size
of an xattr in ext3 is the block size, which is typically 4096 bytes
(that's the maximum too).  The size of an acl entry is 8 bytes, and
after accounting for the xattr header and the acl header, there is room
for about 500 entries in the block.

> - What can I do to define up to 7000 entrys in an ACL?

Are you sure you really want to?  Can you use groups to better manage
access?  Even if you could store 7000 acl entries, there would be a lot
of overhead in reading and processing the acls.

> - Should I use a different filesystem?

That might work.  I know jfs supports larger xattrs.  I'm not sure what
the limits of other files systems are.  I don't know if nfs will work
with too many acl entries either.

Shaggy
-- 
David Kleikamp
IBM Linux Technology Center

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