68 lines
2.4 KiB
Plaintext
68 lines
2.4 KiB
Plaintext
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# sg_compare_and_write.txt
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# This file provides a usage example of sg_compare_and_write.
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# sg_compare_and_write accepts a buffer containing 2 logical instances:
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# - the verify instance: used to match the current content of the LBA range
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# - the write instance: used to write to the LBA if the verify succeeds
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#
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# In case of failure to verify the data, the command will return with check
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# condition with the sense code set to MISCOMPARE DURING VERIFY OPERATION.
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#
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# The following example shows initialization, successful and unsuccessful
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# compare and write using sg3_utils. I am using caw_buf_zero2one and
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# caw_buf_one2zero as shown below.
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$ hexdump /tmp/caw_buf_zero2one
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0000000 0000 0000 0000 0000 0000 0000 0000 0000
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*
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0000200 1111 1111 1111 1111 1111 1111 1111 1111
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*
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0000400
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$ hexdump /tmp/caw_buf_one2zero
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0000000 1111 1111 1111 1111 1111 1111 1111 1111
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*
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0000200 0000 0000 0000 0000 0000 0000 0000 0000
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*
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0000400
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$ sg_map -i -x
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/dev/sg0 0 0 0 0 0 /dev/sda ATA ST3320613AS CC2H
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/dev/sg1 3 0 0 0 5 /dev/scd0 HL-DT-ST DVD-RAM GH22NS30 1.01
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/dev/sg2 5 0 0 0 0 /dev/sdb KMNRIO K2 0000
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/dev/sg3 5 0 0 1 0 /dev/sdc KMNRIO K2 0000
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# First I zero out the volume to make sure that the first compare and write
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# will succeed
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$ sg_write_same --16 -i /dev/zero -n 0x200000 -x 512 /dev/sdc
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$ dd if=/dev/sdc bs=512 count=1 skip=100 2>/dev/null | hexdump
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0000000 0000 0000 0000 0000 0000 0000 0000 0000
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*
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0000200
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$ ./sg_compare_and_write --in=/tmp/caw_buf_zero2one --lba=100 --xferlen=1024 /dev/sdc
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# contents of LBA 100 are a block of ones
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$ dd if=/dev/sdc bs=512 count=1 skip=100 2>/dev/null | hexdump
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0000000 1111 1111 1111 1111 1111 1111 1111 1111
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*
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0000200
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# We repeat the same compare and write command (zero2one input buffer).
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# compare and write fails since the verify failed (compared the zero block to
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# the actual 1 block in LBA 100
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$ ./sg_compare_and_write --in=/tmp/caw_buf_zero2one --lba=100 --xferlen=1024 /dev/sdc
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COMPARE AND WRITE: Fixed format, current; Sense key: Miscompare
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Additional sense: Miscompare during verify operation
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sg_compare_and_write: SCSI COMPARE AND WRITE failed
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# Now we use the second buffer (one2zero)
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$ ./sg_compare_and_write --in=/tmp/caw_buf_one2zero --lba=100 --xferlen=1024 /dev/sdc
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# operation succeeded, contents of LBA 100 are back to zero
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$ dd if=/dev/sdc bs=512 count=1 skip=100 2>/dev/null | hexdump
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0000000 0000 0000 0000 0000 0000 0000 0000 0000
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*
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0000200
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