Re: Exadata backups
- From: Riyaj Shamsudeen <riyaj.shamsudeen@xxxxxxxxx>
- To: mboligan@xxxxxxxxx
- Date: Tue, 29 Oct 2013 12:25:20 -0700
I think, performance improvement Alan noticed, is probably due to the IB
network. ZFS appliances are directly connected to the IB network (compute
and storage nodes are connected to the IB network, as you know).
For level 0 backups, rman channels must read the blocks from the cellserv
to compute nodes and then write to the ZFS appliance (which is usually
mounted as NFS file system). Both read and write calls flows through IB
network, however, data flow is: request from compute node(s) -> blocks from
cellserv -> compute nodes -> written to ZFS file system, data flow
contained in the IB network.
For incremental level 1+ backups, there are some optimization, blocks which
do not qualify for backup are not read in to the compute nodes at all, i.e.
cellserv does block filtering. Also, (If I recall correctly) the block
level change tracking mechanism works at block level in exadata(rather than
group of blocks as in non-exadata) and so, blocks without recent activity
can be completely eliminated in the cellserv layer itself.
Of course, HCC helps to reduce the size of the database.
To answer your question directly, another advantage with ZFS is that it
supports HCC compression. So, you could potentially take a ZFS backup and
mount that as a database (but require little bit tweaking to the backups
though). But, you can't do that with EMC server.
Cheers
Riyaj Shamsudeen
Principal DBA,
Blog: http://orainternals.wordpress.com
OakTable member http://www.oaktable.com and Oracle ACE Director
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