Date: Tue, 05 Feb 2008 08:38:25 -0500 From: Nick Gustas <freebsd-stable@tychl.net> To: Joe Peterson <joe@skyrush.com> Cc: freebsd-fs@freebsd.org Subject: Re: Forcing full file read in ZFS even when checksum error encountered Message-ID: <47A866D1.3040703@tychl.net> In-Reply-To: <47A864D9.4060504@skyrush.com> References: <47A73C8D.3000107@skyrush.com> <86prvby5o1.fsf@ds4.des.no> <47A864D9.4060504@skyrush.com>
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Joe Peterson wrote: > Dag-Erling Sm=C3=B8rgrav wrote: > =20 >> Joe Peterson <joe@skyrush.com> writes: >> =20 >>> When I try to copy the file, I get only 655360 bytes copied, and then= the copy >>> stops. I assume this is because the next block is where the error is= . >>> =20 >> Try to lseek past it. >> =20 > > Well, I'd like to actually read the "bad" data too, so I can see if it = is > really bad or if there is a metadata issue. Basically, I'd like to rec= over > all the file's bytes this once without having ZFS stop me due to the ch= ecksum > failure, just for debugging purposes. Is this impossible in ZFS? > > -Thanks, Joe > =20 This may do what you want, but I'm not sure if this only disables=20 creation of checksums, or it disables use of preexisting checksums=20 entirely. The man page entry would suggest it disables them for reads=20 too. If this is the case, it should do what you want. http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#Chec= ksums Verify the type of checksum used: zfs get checksum <filesystem> Tuning is achieved dynamically by using: zfs set checksum=3Doff <filesystem> And reverted: zfs set checksum=3D'on | fletcher2 | fletcher4 | sha256' <filesystem> Fletcher2 checksum (the default) has been observed to consume roughly=20 1Ghz of a CPU when checksumming 500 MByte per second. Man page: checksum=3Don | off | fletcher2, | fletcher4 | sha256 Controls the checksum used to verify data integrity. The=20 default value is "on", which automatically selects an appropriate=20 algorithm (currently, fletcher2, but this may change in future=20 releases). The value "off" disables integrity checking on user data. =20 Disabling checksums is NOT a recommended practice.
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