RE: Reality check for filesystem/disk layout

Readahead is important for archiving - you want to avoid head seeks between two spindles, and on arrays where your physical disk could be shared between multiple volumes, it becomes extra important to bundle as much i/o per head read as possible, since that I/O can adversely affect other volumes as well. And since you know a read off a redolog is going to be a sequential read, it makes sense to optimize for that I/O pattern.

Thanks,
Matt

--
Matthew Zito
GridApp Systems
Email: mzito_at_gridapp.com
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> -----Original Message-----

> From: ml-errors_at_fatcity.com [mailto:ml-errors_at_fatcity.com] On 

> Behalf Of Mladen Gogala

> Sent: Friday, September 26, 2003 3:25 PM

> To: Multiple recipients of list ORACLE-L

> Subject: RE: Reality check for filesystem/disk layout

> 

> 

> Can  you remind me, what is readahead good for on redo files? 

> I believe that parallelism is much more essential for 

> the recovery and archiver file is usually quick enough, even 

> without any special tricks.

>  

>  

> --

> Mladen Gogala

> Oracle DBA 

> 

> 

> -----Original Message-----

> Matthew Zito

> Sent: Friday, September 26, 2003 3:05 PM

> To: Multiple recipients of list ORACLE-L

> 

> 

>  

> Avoid small stripe sizes for your redo log volumes - 

> especially on two-disk-only RAID sets, you'll break readahead 

> and write allocation on many arrays.  

>  

> Beyond that, it looks good - what kind of array are you using?

>  

> Matt

> 

> --

> Matthew Zito

> GridApp Systems

> Email: mzito_at_gridapp.com

> Cell: 646-220-3551

> Phone: 212-358-8211 x 359

> http://www.gridapp.com <http://www.gridapp.com/>  

> 

> -----Original Message-----

> JayMiller_at_tdwaterhouse.com

> Sent: Friday, September 26, 2003 1:30 PM

> To: Multiple recipients of list ORACLE-L

> 

> 

> We have the luxury of moving a 300G database to a new box 

> that's being built and choosing the specifications, disk 

> layout, striping, etc.  After spending the morning poring 

> over Cary Millsap's wonderful VLDB  paper this is what we're 

> thinking of but I'd appreciate any comments.

>  

> One of my main goals going in was separating redo logs into 2 

> sets of disks and archive logs on a third.

>  

> We have 16 disks to play with and seem to be winning the 1+0 

> battle against some SAs who don't understand why we wouldn't 

> want to use RAID5.

>  

> The database has minimal write activity during the day (other 

> than sorts to the temp tablespace) but huge batch write 

> activity at night and especially at the end of the month (the 

> data load time is enough of a problem that the few 

> partitioned tables we can easily reload are doing 

> unrecoverable loads). There is a lot of read activity during 

> the day, both single row queries from front ends that are 

> rolled out to several thousand people and reports that can do 

> some large sort/merge joins.

>  

> Here's what we were thinking:

>  

> 1st Disk Set - 4 72M disks RAID 1+0

>  

> 1st and 3rd redo log on outside

> Misc. Datafiles in middle

> Misc scripts and files used by other departments in center

>  

> 2nd Disk Set - 6 72M disks RAID 1+0

> Archive logs on outside

> Temp tablespace and misc. datafiles in middle

> Text files used for loading in center

>  

> 3rd Disk Set - 6 72M disks RAID 1+0

> 2nd and 4th redo logs on outside

> Rollback tablespace and misc datafiles in middle

> /oracle (executables and some scripts) in center

>  

>  

> I was debating if there was any advantage in varying stripe 

> sizes across the different disk sets (since I know Cary says 

> redo logs like fine grained stripe sizes) but given the mix 

> of uses for each that doesn't seem viable=

> 


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