zdb question

[Dave Baukus]

On 3/4/19 9:49 AM, Dave Baukus wrote:
> On 3/1/19 3:01 AM, Andriy Gapon wrote:
Thanks for your input.
>> On 28/02/2019 15:59, Dave Baukus wrote:
>>> If one uses zdb -R <pool name> <dva> to read the contents of every disk block
>>> associated with the DVA in a raidz2 pool then does one expect the
>>> dump of each DVA to be the exact USER WRITTEN contents of the file ?
>> I think so; on a condition that the DVA refers to the file's data block (L0).
>>
>>> Or does this usage of zdb pull in the raidz2 checksum blocks and/or padding ?
>>> Looking at the code, I don't think so.
>>>
>>> I ask because I have a file of known contents (every byte was written as 0x42 == 'B'),
>>> and if I execute the script below and redirect the output to a file then
>>> the contents of the output file has chunks of non-B characters.
>>>
>>> For example:
>>>
>>> Offset 300000, DVA 1:9f08e2ff000:120000
>> How did you come up with this DVA?
>> Are you sure about the size component?
All DVAs were from zdb the output of  zdb -dddddd  <obj set> <obj id>
All DVAs examined were L0 DVAs and the size is correct (I assume as the
size comes from zdb -ddddd).
The pool has a record size of 1M.

I'll have to dig into it when time allows ...

>
>>> Found vdev type: raidz
>>>
>>> 1:9f08e2ff000:120000
>>>             0 1 2 3 4 5 6 7   8 9 a b c d e f  0123456789abcdef
>>> 010000:  01000321b60d0000  0afb2f931d805100  ....!....Q.../..
>>> 010010:  02ac211c00020f00  00e2000680110031  .....!..1.......
>>> 010020:  39345f58656c6966  0f001334322e3639  fileX_4996.24...
>>> 010030:  050040cb1f0c0002  02020c003a35352f  ..... at ../55:....
>>> 010040:  3822050040ea1f00  210c00020f002136  ... at .."86!.....!
>>>
>>> -----
>>>
>>> Whereas I expect every DVA chunk to look like:
>>>
>>> Offset 0, DVA 1:9f08e0bf000:120000
>>> Found vdev type: raidz
>>>
>>> 1:9f08e0bf000:120000
>>>             0 1 2 3 4 5 6 7   8 9 a b c d e f  0123456789abcdef
>>> 000000:  4242424242424242  4242424242424242  BBBBBBBBBBBBBBBB
>>> 000010:  4242424242424242  4242424242424242  BBBBBBBBBBBBBBBB
>>> 000020:  4242424242424242  4242424242424242  BBBBBBBBBBBBBBBB
>>> 000030:  4242424242424242  4242424242424242  BBBBBBBBBBBBBBBB
>>> 000040:  4242424242424242  4242424242424242  BBBBBBBBBBBBBBBB
>>>
>>> ----
>>>
>>> On the other hand, if I use a simple program to read the file and verify that every byte
>>> is 0x42 then no errors are reported.
>>>
>>> What gives ?
>>> Am I misusing zdb ?
>> Perhaps.
>>
>