XPWRITE data integrity

Jim.Coomes at seagate.com Jim.Coomes at seagate.com
Mon Dec 15 14:28:05 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* Jim.Coomes at seagate.com
*
The incorporation of the data integrity proposal into SBC-2 raises a
question: how does XPWRITE function with data integrity? Below are several
possible approaches. Please voice your opinions to the reflector or to me
offline.

Simple function

The simple approach would be to require the protection information on the
parity drive be the XOR product of the protection information on the data
drives. In this case, little checking of the protection information is
possible. The only checking may be the guard field if the CRC is not
seeded.

With this XPWRITE function the protection information for a failed data
drive would be regenerated the same way as the user data, XOR product of
the parity drive and the remaining data drives.

Robust function

To validate the transfer of data to and from the parity drive, the same
functionality as for normal writes and reads could be required. The 3 bit
WRPROTECT field could be added to the XPWRITE command. The parity drive
would check the protection information as specified by the WRPROTECT field.
The parity drive would write the protection information to the media
without XORing with the previous protection information. A read access to
the parity drive could check the protection information as specified by the
RDPROTECT field in the read command.

With this XPWRITE function the protection information for a failed data
drive would have to be recalculated.

Jim Coomes

952-402-2665



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