[Gluster-users] Concepts of Gluster: Block- vs File-based | How does cluster internally work?

Amar Tumballi amar at gluster.com
Thu Nov 25 05:59:16 UTC 2010


Hi Jens,

Read Inline..


> Some of my Questions:
>
> 1.) When requesting a file, is the whole file retrieved or only a portion
> of
> the file?
>

Gluster has 1-1 mapping between client side posix calls to server side posix
calls. ie,
when a open is called on client mount point, it will be translated to a open
on server
side (where the file actually resides). Answer for your question will be you
will get the
portion of file you requested for, and not whole file.


> 2.) Are random File accesses supported?
>

Yes. But, considering scenario in case of Databases, which is, random file
accesses with
query(read) for very small blocks, network delay and context switch delays
involved will
make the performance suffer.


> 3.) How does cluster internally Workd when the Database (liek MySQL) create
> a large file and then accesses this file? Does Cluster shomehow operate on
> a
> "Block Level"? How will an index-scan be translated in reagards how gluster
> will access the data on the remote system?
>
>
As I told in case of 1, Gluster will do 1-1 operation which is done @ the
mount point
over the server, hence the main issue again will be latency of the network
in all these
operations.



> I am very thankfull for any information (also links...) that help me to
> understand how gluster internally handles "file accesses" .
>
>
Lets be clear on what 'file accesses' means. I am taking it as 'read'
(considering its a
database and there will be lot of queries), but there are multiple system
calls which can
mean the same with respect to filesystem, like, access(), lookup(), stat(),
open()...


Regards,
Amar


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