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A few commands will show you how safe your data is...
Create a disk in a file and copy some data
cd ~/Desktop
hdiutil create -size 100m -type UDIF -fs HFSXJ -volname jollystest jollystest
hdiutil attach jollystest.dmg
/dev/disk8 GUID_partition_scheme /dev/disk8s1 Apple_HFS /Volumes/jollystest
cp /sbin/* /Volumes/jollystest/
shasum /Volumes/jollystest/* >jollystest.sum
umount /Volumes/jollystest
Now create a fault by writing random data to the diskfile
dd if=/dev/random of=jollystest.dmg bs=4k seek=4000 count=1000 conv=notrunc
1000+0 records in 1000+0 records out 4096000 bytes transferred in 0.473120 secs (8657424 bytes/sec)
hdiutil attach jollystest.dmg
/dev/disk8 GUID_partition_scheme /dev/disk8s1 Apple_HFS /Volumes/jollystest
diskutil verifyVolume /dev/disk8s1
Started file system verification on disk8s1 jollystest Checking file system Checking Journaled HFS Plus volume Detected a case-sensitive volume Checking extents overflow file Checking catalog file Checking multi-linked files Checking catalog hierarchy Checking extended attributes file Checking volume bitmap Checking volume information The volume jollystest appears to be OK Finished file system verification on disk8s1 jollystest
Remember, diskutil just stated "appears to be OK"
shasum --check jollystest.sum
/Volumes/jollystest/SystemStarter: FAILED /Volumes/jollystest/autodiskmount: OK /Volumes/jollystest/disklabel: OK /Volumes/jollystest/dmesg: OK /Volumes/jollystest/dynamic_pager: OK /Volumes/jollystest/emond: OK /Volumes/jollystest/fibreconfig: OK /Volumes/jollystest/fsck: FAILED /Volumes/jollystest/fsck_cs: OK /Volumes/jollystest/fsck_exfat: OK /Volumes/jollystest/fsck_hfs: FAILED /Volumes/jollystest/fsck_msdos: OK . . . /Volumes/jollystest/shutdown: OK /Volumes/jollystest/umount: OK shasum: WARNING: 3 of 60 computed checksums did NOT match
/
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