[Gluster-users] Is read cache a file cache or a block cache?

[Anand Avati]

The cache works by remembering 128KB "pages" within files. Effectively
"blocks" in your terminology.

Thanks

On Wed, 11 Mar 2015 at 12:36 Jon Heese <jonheese at jonheese.com> wrote:

> Hello,
>
> I have a two-server, two-brick (one brick per server) replicated Gluster
> 3.6.2 volume, and I'm interested in the 'performance.cache-size' option
> and how that read cache works.
>
> My volume currently stores a handful of ~500GB image files, which are
> then fed to an iSCSI daemon to serve up datastores and other
> miscellaneous iSCSI disks to servers over an iSCSI network.
>
> I have about 14GB of unutilized (minus system cache/buffers) memory on
> the gluster servers (which are also the gluster clients, in this case)
> which I'd like to utilize to improve the read performance of this volume.
>
> So since my files are are well over the "tens of GB" mark, I'm curious:
> Does the Gluster read cache work at the block level -- i.e. caching
> *blocks* that are likely to be read -- or does it work at the file level
> -- caching *files* that are likely to be read?  Obviously, the latter
> might work well for me, but the former is likely not very useful.
>
> I've tried searching around for details on how this works, but short of
> diving into the code itself (which is likely beyond my skill level and
> time allowance), I haven't been able to find the answer to this question.
>
> If I've misunderstood how any of this is supposed to work, please feel
> free to correct me.  Thanks in advance!
>
> Regards,
> Jon Heese
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