[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;
Nikita.
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