Can't read a full block, only got 8193 bytes.

Ask Bjørn Hansen ask at
Thu Feb 23 08:56:31 UTC 2012

On Feb 19, 2012, at 12:10, Artem Belevich wrote:

>> "Can't read a full block, only got 8193 bytes."
> That's probably just a side effect of ZFS checksum errors. ZFS will
> happily read the file until it hits a record with checksum. If
> redundant info is available (raidz or mirror), ZFS will attempt to
> recover your data. If there's no redundancy you will get read error.
> If you do "zpool status -v" you should see list of files affected by
> corruption.

Hi Artem,

Thank you for the reply and the tips!   

That makes sense and explains why we'd just get checksum errors on a raidz1 test (but bonnie++ was happy except things were slow), but had the weird errors on a single disk pool.

>> This seems to only be when testing a single ZFS disk or a UFS partition.  Testing a raidz1 we just get checksum errors noted in zpool status, but no errors reading (though read speeds are ~10MB/second across four disks -- writing sequentially was ~230MB/second).
>> Any ideas where to start look?
> You need to figure out why you're getting checksum errors. Alas
> there's probably no easy way to troubleshoot it. The issue could be
> hardware related and possible culprits may include bad RAM, bad SATA
> cables, quirks of particular firmware revision on disk controller
> and/or hard drive.

Replacing the 3ware controller with a basic LSI controller fixed the problems and improved performance, so I guess the 3ware controller doesn't play nice with the Seagate 3TB disks (they're not on their compatibility list).


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