Re: Raw Disk Partition vs. Unix File System (Oracle 6)

In article <1993Aug16.224048.15479_at_lmpsbbs.comm.mot.com> cds016_at_isadmin1.comm.mot.com (David Schmitt) writes:
>In article <CBuyrL.DLo_at_cbnewse.cb.att.com>,
>richard.dib <cafe_at_cbnewse.cb.att.com> wrote:
>>
>>Here are my questions:
>>
>>- Does anybody have any experience with Oracle using a raw disk partitition
>> instead of the Unix file system? Could you share your experiences?
>
>I've used raw devices with Oracle 6 for several years, and only had one
>bad experience (when a system admin put swap space on top of a data file).
>It is more difficult to administer in many environments, since it is hard
>to adjust disk layout on the fly (you typically have to reslice your disk).
>However, with planning I haven't found this to be that much of a problem.

Planning is the key word, My major complaint about people that stand up and say "Lets Go Raw" is that they often are not willing to pay the price to implement correctly.

At a large company I was at not to long ago, I had a group of individuals that wanted their dinky 20M of data database raw because they read someplace that is was GOOD. After about 2 weeks of argument I finally said:

OK, How are YOU going to back up your database?

"Oh we thought you would do that"

Not me Jack. I'm a Oracle Geek. If you think I'm going to spent 2 months writing a backup routing that uses a glorified copy command to backup production data while I'm doing my real job AND then bet my furture with this company that it will work, Your nuts. Go write me a routine that handles tape errors, does something to figure out that new datafiles have been added since last time, writes logfiles someplace so we can review them and creates labels so that in in 2 years when we have to recover we know which files sets to put where.

Oh and don't forget to shutdown the database.

I never heard from them again.

I'm not saying that all of the above is not possible, But that people somehow think they get raw for free. They often are not willing to pay the price to to the job correctly and get burned.

>>- What are the benefits? Is the improvement in performance worth the work?
>
>Benefits are improved integrity (don't have to worry about whether UNIX
>buffers were flushed at the time of a crash), and performance improvements.
>I have never benchedmarked the difference in performance, but it makes
>sense to me to believe there is one.

You might want to ask oracle for a paper by Cary Millsap entitled "Making the Decision to Use UNIX Raw Devices". Basically it sez there are cases where raw is the answer but there are a lot of other things to try first.

I'm not sure I agree with the integrity issue. If Oracle uses the O_SYNC options on their writes (they SAY they do) then you should be ensured that data got to atleast the LOGFILE intact and thats all you really need.

I'm also not sure I agree with the performance improvment statement in ALL cases. Seems to me that if you are dealing with large FS blocksizes ie) 32K-64K, then your improvement should be if not negligable then atleast greatly reduces. Further if your dealing with SunOS and have a large amount of RAM that is used as a massive transparant buff cache then the FS could be a win. Depenting on the setup up they may beable to get near raw performance on a cooked db.

Of course all this is numberless theory and should really be backedup with a benchmark. But that would require work and might prove me wrong :-}

[...]

-- 
Regards, 

Lee E. Parsons                  		Baker Hughes Inteq, Inc
Oracle Database Administrator 			lparsons_at_exlog.com