Re: Oracle and Raid setup

"VC" <boston103_at_hotmail.com> wrote in message news:KJmdnatiCLqgWjHfRVn-rw_at_comcast.com...
> Hi,
>
> "Noons" <wizofoz2k_at_yahoo.com.au> wrote in message
> news:42ac5c85$0$14447$5a62ac22_at_per-qv1-newsreader-01.iinet.net.au...
>> Not at all. You are assuming that the OS is capable of somehow discerning
>> from the disk controller where the disk heads are, where they'll be after
>> the next batch of channel programs comes through, what the access pattern
>> from the database will be, and so on. Nothing is further from the truth.
>> Of course it can be done. It just isn't.
>
>
> I see. I need to investigate this issue a bit.
> I've always been under impression that since the read optimization was
> done awhile ago, it surely is done nowadays.
>
> Thank you.
>

It appears that the situation is not altogether bleak, even in the Unix world ;) The SUN volume manager tries to do something about improving mirrored read performance:

"Round Robin (Default)
 Attempts to balance the load across the submirrors. All reads are made in a round-robin order (one after another) from all submirrors in a mirror.

Geometric
 Enables reads to be divided among submirrors on the basis of a logical disk block address. For instance, with a two-way submirror, the disk space on the mirror is divided into two equally-sized logical address ranges. Reads from one submirror are restricted to one half of the logical range, and reads from the other submirror are restricted to the other half. The geometric read policy effectively reduces the seek time necessary for reads. The performance gained by this mode depends on the system I/O load and the access patterns of the applications
 "

EMC Symmetrics and such, of course, optimize access to a mirrored set. It does take into account where the head is currently located (among other things).

I have very little experience with Linux software implemented RAIDS so I'll defer to the experts.

Regards.

>
>
>
Received on Sun Jun 12 2005 - 20:39:57 CDT