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Adaptive PRE_READ

IP.com Disclosure Number: IPCOM000216045D
Publication Date: 2012-Mar-21
Document File: 2 page(s) / 152K

Publishing Venue

The IP.com Prior Art Database

Abstract

In 4K sector format with 512 bytes emulation HDD, un-aligned write performance degrades due to Read-Modify-Write operation. To improve this, adjust disk read length for Read-Modify-Write accroding to the conditions, so that HDD can read the data as much as possible, as far as HDD does not cause the extra revolution.

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Adaptive PRE_READ

Calculate disk read length for Read-Modify-Write (RMW) as follows.


* When write command comes,


1. Set RMW Read start LBA with command start LBA


2. Calculate servo number of RMW Read start LBA (startServo)


* When End Of Track (EOT) comes during RMW Read,

3. Calculate end servo number of RMW Read => readEndServo readEndServo = 2 - Overhead of head change from read to write


4. Calculate servo number of EOT => eotServo


5. Check skew with 3 and 4, and then adjust readEndServo [Refer to Figure 1.]

Figure 1.


6. Check eotServo and EOT servo number of next track (nextEotServo), and then adjust readEndServo [Refer to Figure 2.]

Figure 2.

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7. Convert readEndServo to LBA and start disk read
8-1. Complete disk read
8-2. EOT event occurs before the disk read complete, back to 3

Disclosed by Hitachi Corporation

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