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Diffstat (limited to 'examples/sg_compare_and_write.txt')
| -rw-r--r-- | examples/sg_compare_and_write.txt | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/examples/sg_compare_and_write.txt b/examples/sg_compare_and_write.txt new file mode 100644 index 00000000..86b166b3 --- /dev/null +++ b/examples/sg_compare_and_write.txt @@ -0,0 +1,67 @@ +# sg_compare_and_write.txt +# This file provides a usage example of sg_compare_and_write. +# sg_compare_and_write accepts a buffer containing 2 logical instances: +# - the verify instance: used to match the current content of the LBA range +# - the write instance: used to write to the LBA if the verify succeeds +# +# In case of failure to verify the data, the command will return with check +# condition with the sense code set to MISCOMPARE DURING VERIFY OPERATION. +# +# The following example shows initialization, successful and unsuccessful +# compare and write using sg3_utils. I am using caw_buf_zero2one and +# caw_buf_one2zero as shown below. + +$ hexdump /tmp/caw_buf_zero2one +0000000 0000 0000 0000 0000 0000 0000 0000 0000 +* +0000200 1111 1111 1111 1111 1111 1111 1111 1111 +* +0000400 + +$ hexdump /tmp/caw_buf_one2zero +0000000 1111 1111 1111 1111 1111 1111 1111 1111 +* +0000200 0000 0000 0000 0000 0000 0000 0000 0000 +* +0000400 + +$ sg_map -i -x +/dev/sg0 0 0 0 0 0 /dev/sda ATA ST3320613AS CC2H +/dev/sg1 3 0 0 0 5 /dev/scd0 HL-DT-ST DVD-RAM GH22NS30 1.01 +/dev/sg2 5 0 0 0 0 /dev/sdb KMNRIO K2 0000 +/dev/sg3 5 0 0 1 0 /dev/sdc KMNRIO K2 0000 + +# First I zero out the volume to make sure that the first compare and write +# will succeed +$ sg_write_same --16 -i /dev/zero -n 0x200000 -x 512 /dev/sdc + +$ dd if=/dev/sdc bs=512 count=1 skip=100 2>/dev/null | hexdump +0000000 0000 0000 0000 0000 0000 0000 0000 0000 +* +0000200 + +$ ./sg_compare_and_write --in=/tmp/caw_buf_zero2one --lba=100 --xferlen=1024 /dev/sdc + +# contents of LBA 100 are a block of ones +$ dd if=/dev/sdc bs=512 count=1 skip=100 2>/dev/null | hexdump +0000000 1111 1111 1111 1111 1111 1111 1111 1111 +* +0000200 + +# We repeat the same compare and write command (zero2one input buffer). +# compare and write fails since the verify failed (compared the zero block to +# the actual 1 block in LBA 100 +$ ./sg_compare_and_write --in=/tmp/caw_buf_zero2one --lba=100 --xferlen=1024 /dev/sdc +COMPARE AND WRITE: Fixed format, current; Sense key: Miscompare + Additional sense: Miscompare during verify operation +sg_compare_and_write: SCSI COMPARE AND WRITE failed + +# Now we use the second buffer (one2zero) +$ ./sg_compare_and_write --in=/tmp/caw_buf_one2zero --lba=100 --xferlen=1024 /dev/sdc + +# operation succeeded, contents of LBA 100 are back to zero +$ dd if=/dev/sdc bs=512 count=1 skip=100 2>/dev/null | hexdump +0000000 0000 0000 0000 0000 0000 0000 0000 0000 +* +0000200 + |