Re: Disk Storage

"S.Sathish" <ssathish@getafix.cmc.net.in> wrote in article <6aahth$dq3@cssun.mathcs.emory.edu>... > hi, > The chapter on performance tuning in the book Informix > Unleashed,says 'store the dbspaces which are prime real estate near the > center of the disk' This rule of thumb (ROT) has been around for decades and attempted to reduce service times by forcing the I/O frequency distribution to look like a bell curve. Most disks now pack more data on the outside of the disk than the inside and therefore the low RBA transfer rates are about 50% higher than the high RBA rates. Also, the seek times for the first 2GB are shorter because the 2GB on the outside of the disk span fewer cylinders than the inside. Rotational delays are of course still the same. For example, a Seagate 9GB (sic) 3.5" disk transfers about 10.7 MB/sec at the low RBA and 7.5 MB/sec at the high RBA. Also, with mirrored disks smart read service policies will help compensate for "bad" data placement.