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Re: Cluster file systems versus raw devices in Oracle RAC

From: Maimon Oded <oded.maimon_at_gmail.com>
Date: 2005-12-27 13:40:12
Message-id: afc75c420512270440x6931ad06i4032c1e3d7b6333f@mail.gmail.com


i think that the only reason for using raw devices is if you don't have NAS for nfs or you dont have the cache to get a good CFS.

On 12/27/05, Kevin Closson wrote:
>
>
> In the context of RAC, filesystems cannot be "so powerful" (as was
> stated in the original post), in fact they MUST be 100% passive
> in theat they must offer direct IO.
>
> With direct IO, the best a filesystem can do is get out of
> the way. Direct IO is only sufficient when the code path is as close to
> the raw IO code path as possible. Given that, where is there
> room to be "powerful" ?
>
> A good CFS is, on the other hand, much easier to administer (thingies
> like ASM not withstanding). But there is really no way to measure
> "improved managability"...that is, there are no TPCM benchmarks
> that measure Administrative Tasks per Month :-)
>
> All of the above, however, is in reference to the database component
> files, however. There is much more to an Oracle setup than the
> datafiles. There is Oracle Home, imp/exp,SQL Loader, external tables,
> UTIL_FILE, BFILE, logging, trace, archived logging, ETL, etc, etc.
>
> So folks that don't use a CFS with RAC get to spend their valuable
> time thinking about how to adminster the ancilliary files I
> mention a lot more than those who implement on a CFS environment.
>
> Remember, the technology like GPFS has not been around forever. In
> fact, GPFS was NOT supported on less than 3 nodes until not that long
> ago, due to their split-brain avoidance mechanisms (note to readers,
> get your facts before you bother suggesting this point is not true).
>
> So, the way it has gone, generally, is people have had to leave behind the
> normal, reasonable approach to administration when they went to OPS/RAC.
> They have been forced to leave filesystems behind.
>
> The other problem is that most CFS historically (all of them except
> PolyServe
> and TruClusters CFS in fact) have been implemented with dedicated servers
> for lock management and metadata management. Sort of sounds like a single
> point of failure and a bottleneck, right ? Well, that architecture is
> in fact SPOF and bottlenecked. Taking something as available as RAC and
> stuffing
> it into an SPOF fileystem makes very little sense.
>
> I know, I know, some of you will point out that the latest-latest
> release of this-or-that CFS have just introduced a distributed lock
> manager thus eliminating the SPOF...well, I guess better late than
> never huh ? :-) And nothing like cramming the right architecture
> into a product well after it is in the field, huh ?
>
> OK, flame suit on.... let's have it :-)
>
>
> >>>-----Original Message-----
> >>>From: oracle-l-bounce_at_freelists.org
> >>>[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Antonio Belloni
> >>>Sent: Monday, December 26, 2005 10:03 AM
> >>>To: oracle-l_at_freelists.org
> >>>Subject: Cluster file systems versus raw devices in Oracle RAC
> >>>
> >>>Hi,
> >>>
> >>>Does anyone using cluster file systems in a RAC 10gR2
> >>>installation, specifically IBM's GPFS?
> >>>
> >>>I've visited a company that is running RAC 10gR2 in AIX over
> >>>raw devices. Why someone would choose to use raw devices ,
> >>>with all the problems to administer , when all the modern
> >>>file systems are so powerful? Is there any issues when using
> >>>cluster file systems + RAC? Is there considerable
> >>>performance benefits when using raw devices with RAC ?
> >>>
> >>>I┤ve always used Oracle stand alone instances over file
> >>>systems (since version 7) , and performance was always very
> >>>good. I┤ve tested raw devices almost 10 years ago , and even
> >>>in that time (the hardware today is much better - SAN , 15K
> >>>rpm disks , huge caches - and the file systems software
> >>>today is much better) the cost to administer it does not
> >>>compensate the benefits (only 5% more faster than file
> >>>systems in Oracle 7).
> >>>
> >>>So , as I didn't see a line in the Oracle RAC documentation
> >>>saying that RAC only works over raw devices and besides any
> >>>limitations imposed by RAC , why use raw devices nowadays ?
> >>>
> >>>Regards,
> >>>Antonio Belloni
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>_______________________________________________________
> >>>Yahoo! doce lar. Faša do Yahoo! sua homepage.
> >>>http://br.yahoo.com/homepageset.html
> >>>
> >>>--
> >>>http://www.freelists.org/webpage/oracle-l
> >>>
> >>>
> >>>
> --
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>
>
>
Received on Tue Dec 27 2005 - 13:40:12 CST

Original text of this message

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