[Lustre-devel] New Pools DLD

Nikita Danilov Nikita.Danilov at Sun.COM
Tue Apr 22 10:03:59 PDT 2008

Eric Barton writes:
 > Comment in-line below...
 > > -----Original Message-----
 > > From: lustre-devel-bounces at lists.lustre.org 
 > > [mailto:lustre-devel-bounces at lists.lustre.org] On Behalf Of 
 > > Andreas Dilger


 > > Since we are already need to change the LOV_MAGIC value, we may as
 > > well do as you suggest and have 0x0BD3ssss instead of 0x0BD30BD0,
 > > where ssss = size of EA in bytes.
 > That seems a hack - why overload magic like this rather than have a
 > separate field?

Historically space in EA's was very scarce resource. Also, even a slight
increase in EA size might result in significant performance changes,
e.g., when EA's stop fitting into inode, and additional seek+read is
added to every inode load. So I tend to agree with Andreas that it makes
sense to replace __u32 magic with

        __u16 layout_type_id;
        __u16 layout_descriptor_size;


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