Feature Desc riptions
6- 4 Maxt or Atl as 10K III
A 10,000 rpm rotation speed yields an average latency of 3 ms.
Embedded servo information is written in a spoke configuration on every track, on
every disk surface. The spokes (or headers) consist of quadrature analog patterns and
digital addr ess da t a. The digit al por ti ons of the sp oke da ta ar e read and us ed to loca te
the desired track, spoke, and head number. The quadrature analog signal portion is
detected and used by a se rv o feedba c k cont r ol l oop to prec i sel y po sition the head on
th e tr a ck cent e r.
The di sk drives use a c ombina t i on of pa r ity c hecking, er ro r de t ect i on c oding (EDC),
error corr ection co ding (ECC), and checkpoin ting to prot ect stored da ta from media
er ro rs , tran s fer o r add re s si n g erro rs , or errors in tro d u ced d u ri n g bl o ck re allo c ati o n .
To ensure that data read is the same as data written, the drive computes and appends
an Error Correction Code (ECC) to each block of data stored. The drive uses a 352-
bit Reed Solomon code with a 4:1 interleave, which can correct up to 20 bytes in
each block.
The drive can also correct up to 2 bytes per interleave (up to 8 per block) in hardware
(“on-the-fly”), with no loss in throughput.
An end-t o-e nd er r or detection code (EDC) protects data f r om a ny error s i ntroduc ed
by internal buses, the disk controller chip, the data cache, or the SCSI interface.
An EDC is calc ula ted and added t o each da ta bloc k a s t he data ar ri ves fr om t he SCSI
bus (aft er SCSI bus par ity is checked). The EDC is st ored with t he data and pr otected
by the block ECC for added securit y. On reading or writing , the EDC is checked as
the data is transferred between buffer RAM and the media or the SCSI bus.
Each data block on the media is identified and located by a servo spoke address. The
spoke addre ss consi sts of a t wo-byte w ord. Each spo ke has mult iple cop ies of the le ast
significant bytes of the address. The disk hardware requires that a majority of the
copies agree and that the result agrees with the ex pected head, track, and spoke
nu mb e r, b e fo re it will read o r wr i te th e d ata.
To further protect against addressing errors, the logical address (LBA) of the data is
added to the EDC of each block. If data is written to the wrong block and
subsequently read, or read from the wrong block, the error will be flagged.
The hardwa re do es not allow a blind r ead of a data block; t he f irmwar e must request
specific data blocks. Even if the head selection hardware malfunctions, it is not possible
for the driv e to return data from the wrong head.