Hi,
I may have experienced some odd behavior from ZFS running 8.0-STABLE-201004
amd64.
I have a zpool 'zhome' on my laptop with checksum=on and copies=2. I was
getting ready to burn a FreeBSD DVD today and was verifying the checkums of the
image I downloaded (stored
on zhome). I got a match on the md5 hash, but a mismatch on the sha256 hash.
Rerunning the sha256 hash gave the correct result. I luckily just got in the
office earlier and had a
zpool status in my terminal buffer which indicated no errors on zhome. Running
zpool status after the checksumming operations shows one checksum error.
I was under the impression that ZFS, upon encountering a checksum error, would
check the second copy of the block (since I have set copies=2) and send that
data instead (assuming it
was correct), that does not seem to have happened. I have run into checksum
errors in the past where I had copies=1, in those cases ZFS would simply stop
reading the file at that
point and I would get a read error, which I did not in this case. Also I am
fairly certain that the dvd image was not buffered in RAM between hashes (i.e.
each hash read the data
from disk).
Perhaps the checksum was correct the first time around and some other part of
my system corrupted the data? RAM has been tested many months ago using
memtest86 and several other
tools without problem (not that new problems couldn't have popped up).
a...@moony:~$ zpool status zhome
pool: zhome
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
zhome ONLINE 0 0 0
ad4p3.eli ONLINE 0 0 0
errors: No known data errors
a...@moony:ISOs$ grep *8.0*amd64-dvd1* CHECKSUM.* | cut -d\= -f2
227adf4b4010aa1bc98baf50953ec2d0
4c087a9d23a53f861f3548461cde500a6db709ff704e972c51677531ea6d65b3
a...@moony:ISOs$ md5 FreeBSD-8.0-STABLE-201005-amd64-dvd1.iso | cut -d\= -f2
227adf4b4010aa1bc98baf50953ec2d0
a...@moony:ISOs$ sha256 FreeBSD-8.0-STABLE-201005-amd64-dvd1.iso | cut -d\= -f2
4fcbcaacf14ff7c0394f119b1ca93e645456241d5b7d42aaf8f92b5a70b279d4
a...@moony:ISOs$ sha256 FreeBSD-8.0-STABLE-201005-amd64-dvd1.iso | cut -d\= -f2
4c087a9d23a53f861f3548461cde500a6db709ff704e972c51677531ea6d65b3
a...@moony:ISOs$ zpool status zhome
pool: zhome
state: ONLINE
status: One or more devices has experienced an unrecoverable error. An
attempt was made to correct the error. Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
using 'zpool clear' or replace the device with 'zpool replace'.
see: http://www.sun.com/msg/ZFS-8000-9P
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
zhome ONLINE 0 0 0
ad4p3.eli ONLINE 0 0 1
errors: No known data errors
a...@moony:ISOs$
-akm
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