Re: ODA 12.1.2 Databases on ACFS
Date: Mon, 26 Jan 2015 07:07:46 -0500
Message-ID: <54C62E12.8050605_at_yahoo.com>
On 01/25/2015 11:40 PM, Seth Miller wrote:
> As of release 12.1.2.0 of the ODA software, all database are created
> on ACFS (CloudFS) by default.
>
> Has anyone implemented this strategy outside of the ODA?
>
> If you have used this on ODA or otherwise, do you have any feedback on it?
>
> Are you utilizing the snapshot ability?
>
> Seth Miller
I have tested ACFS on a normal Oracle 12c RAC system with 2 Dell boxes, connected to a NetApp filer. The systems were running RHEL 6.5, 64bit. LUNs were "scsified" (no ASMLib) and put into ASM. The kernel had no problems building the ACFS drivers and the database performance was quite good, but there . ACFS One notable omission is that there is no defragmenter, which is not very important for a database, but is important if you want to keep other types of files which are frequently created and deleted, like archive logs. Snapshots, however, are CoW (copy on write) and that method has known drawback of tripling the IO rate for writes because the kernel has to do the following:
- Read the old data
- Write the old data to the snapshot pool location
- Write the new data.
That is what "copy-on-write" means. You will do that for every FS block
and for every snapshot. If there are two snapshots of your database, the
system will do 6 IO operations for every write request. With all due
respect to Dell, their IO throughput is not unlimited, so the whole
thing slows down considerably. Fortunately, SAN manufacturers, like
NetApp have much smarter strategy known as "deferred write snapshot"
which was used instead.
Personally, I have installed Oracle 12c on Fedora 20 with Brtfs,
precisely in order to test snapshots. The results show the same problem
as above. My desktop box slows down to a crawl when inserting a million
rows into the database using Perl script to avoid the well known PL/SQL
optimization with commits within the loop. In addition to that, once you
use the files on ACFS, there is no balancing keeping the files populated
to the same level. Since this was only a test configuration, the
production DB is still running 11.2.0.4, the client eventually decided
to use ASM instead of ACFS. I have no experience with ODA, but my
understanding is that it is a Linux box with Oracle, ASM & ACFS, no RAC.
-- Mladen Gogala Oracle DBA http://mgogala.freehostia.com -- http://www.freelists.org/webpage/oracle-lReceived on Mon Jan 26 2015 - 13:07:46 CET