[Lustre-discuss] Maximum MDT Size

[Roger Spellman]

Sorry, I meant max MDT size (I changed the subject).

I guess that my questions are:
1.  What is the maximum number of files I can get on an MDT with
ldiskfs?
2.  What parameters need to be modified to achieve this?
3.  What is the maximum number of files I can get on an MDT with ZFS?
4.  What parameters need to be modified to achieve this?

> -----Original Message-----
> From: Andreas Dilger [mailto:andreas.dilger at oracle.com]
> Sent: Monday, October 18, 2010 5:00 PM
> To: Roger Spellman
> Cc: lustre-discuss at lists.lustre.org
> Subject: Re: [Lustre-discuss] Maximum OST Size
> 
> On 2010-10-18, at 14:47, Roger Spellman wrote:
> > In Lustre 2.x, what is the largest number of files that we could
> possibly have?
> >
> > I noticed that mkfs.lustre on the MDT passes the following
parameters to
> mkfs.ext2:  -i 4096 -I 512
> 
> Do you mean the maximum OST size (as mentioned in the subject) or the
> maximum MDT size (above)?  For the ext4-based ldiskfs the maximum size
is
> 16TB and 4B inodes (this listed in the manual).
> 
> > Can these params be smaller?
> 
> For the MDT, yes, you could potentially use "-i 1500" as about the
minimum
> space per inode, but then you risk running out of space in the
filesystem
> before running out of inodes.  The "-I 512" parameter controls the
size of
> the inode itself, which holds the xattrs.  If there are single-striped
> files and no use of ACLs, user_xattrs, etc. then you might get by with
"-I
> 256", but if this xattr space is exceeded then each such inode will
> consume 4096 bytes of space and also be slower to access.
> 
> > Can we get more inodes if we use zfs?
> 
> Definitely yes.
> 
> Cheers, Andreas
> --
> Andreas Dilger
> Lustre Technical Lead
> Oracle Corporation Canada Inc.