There is a thread on AskTom about where to place data on the disk. The question is why one should place data on the outside of the disk and if that helps performance. I just like to add my view on that discussion. The number of physical I/Os per Disk is limited by the (full/average) seek time. The seek time is the biggest component of the I/O time (with normal Oracle blocksize). The Full Seek Time (seeking from the outermost track to the innermost track or vice versa) can be greatly reduced by only using the outermost tracks on a disk. Why the outermost tracks? Well there is this statistic that on the 1/3 of the outermost tracks there is around 50 percent of the disk capacity stored. If I only have to seek 1/3 of the distance to reach 50 percent of the data all the time, the average seek time will be greatly reduced. If the Seek time is greatly reduced, the total I/O time is greatly reduced and we can do more random I/O operations per second. So to summarize:
1) Use around 50 percent of the disk capacity (outer 1/3 of the tracks)
2) That will increase the number of random I/Os greatly.
It doesn't matter of you use SAN, NAS or JBOD, it is the same principle. Well with SAN and NAS you may not know where your data is located :-) But that is a completely different story.
Sunday, June 12, 2005
Subscribe to:
Post Comments (Atom)
29 comments:
The classic view was also that the outer 1/3 of the disk not only has a higher linear speed past the heads but also higher density. Therefore you got faster transfer speeds in that area of the disk. I have not measured this with the latest multi-100Gb disks, but it was certainly true for older drives in the 10s of Gb size and smaller.
Disk makers usually have free download utils in their sites to test IO speeds. There are also a few utils used to test speed for video editing that can be used to check what is faster where.
Block size (or more appropriately: IO request size) also has a marked effect on performance, particularly where DMA is being used to transfer the data: the more the request size is aligned with the optimal memory access size, the faster the IO will be. This is extremely relevant for PC-class hardware, less so for big iron servers.
Hi Anjo,
Well, I guess that disks have not changed much since the olden days of the 1980's, when you deliberately placed "hot" data files in the middle absolute track to minimize seek delay:
http://www.dba-oracle.com/art_dbazine_disk.htm
You know what frosts me are the huge sizes of disks today.
I wish I could get ten 20 gig disks instead of having to buy these 144 gig monsters. . .
Of course, placing files (their temperature would not matter) in the middle of the disk will only help for the classical scenario:
- 1 disk (possibly containing more platters)
- OS and application on that disk.
Yes, old trick of the trade: your swap space should be in the middle of your OS mount points, thus making delays because of head movements to and from the swap area minimal. I know IBM's LVM in AIX still has the option to postion partitions physically on the outer, middle or inner region of a disk.
But why would you place "hot" files in the middle? How would that affect seek time? Not much, I would say, as there's no telling where the head came from.
But, hey, spindles = speed, that is still true.
Using the middle of the disk can be justified if the seek time outweighs the read time.
Whenever I've had to do that level of tweaking, the winning strategy has always been the same. Put the high IO rate random reads on the fast outside, and slow and sequential on the inside. Numerous faster random reads should be more frequent than big multiblock reads.
Wow This is Deep..I know all of this sounds good but if you really want to change yourself or someone important to you. If you need free tarot in your life. If You can say no to all this free tarot...
I am changing the way I live today ..Think it and believe it.. You can Change Your Life and Start Living Your Dreams Today..http://gregvb.tarotmind.hop.clickbank.net
Hello,
Had to write to let you know that I found your site very useful to me. Could you please tell me how I could find out more? I�d love it if I could get an RSS feed from your site to mine. Is this possible?
Thanks,
start online business
motivation books what about it..motivation books Here it is now its up to you...
employee books
Yo Anjo
If the "good Old days" IBM used to place hot block in the middle of the phycical disk, and this was due to that the phycical head placed here when the disk was Idle to have the shortes fullstrike when beeing activated again, But I don´t recall to have seen this specified for any of the new disk, but I would think that this still apply to some disk types.
So we are back to that it DEPEND on your application and use of thise that determine the location of data on the phycical disk..
;-}
Royalty Free Beats For One Dollar
At
http://upbeat.tk
Nice blog!
If you get a chance, check out my site: Pick 3 Turbo Player
Thanks
Very cool design! Useful information. Go on! Angeles botox los treatment Devil answering machine ford focus body kits
best regards, nice info Thermography business cards manufacturer quickie wheelchairs Transaction merchant services Neurogenic syndromes and botulinum toxin maverick ice cream machines business card printer machine creating designs for business cards Pasadena facelift business card printers Spa heater part
Where did you find it? Interesting read film editing schools
You have an outstanding good and well structured site. I enjoyed browsing through it »
Dear administrator:
Some of our comments above may include links that are no longer valid or that do not have a nofollow value. They might very well lead you today to a third party. Therefore,
I ask you, if you would be so kind, to please delete or disregard those
comments.
Many thanks and best wishes,
Iza, Roberto Iza
Muy Señores Míos:
Algunos de nuestros comentarios incluyen vínculos rotos que bien pudieran llevar hoy a una tercera persona. Por tanto, le rogamos, por favor, que los deseche o desestime.
Gracias y recuerdos
Iza, Roberto Iza
FLz2Uu Your blog is great. Articles is interesting!
SAVvxT Wonderful blog.
Nice Article.
Please write anything else!
Good job!
Magnific!
Thanks to author.
Nice Article.
Nice Article.
Thanks to author.
W2qN2U Please write anything else!
actually, that's brilliant. Thank you. I'm going to pass that on to a couple of people.
I had my first headhunt in the curikudos job fair held in 2006. And now i think its time to switch over. Can some one let me know when the job fair starts again.
Post a Comment