Software RAID issues (was Re: Suggestions solicited, server bring up)

[dan]

Ben Scott wrote:
> On Tue, Nov 24, 2009 at 2:32 PM, Ken D'Ambrosio <ken at jots.org> wrote:
>   
>> UDNRC [sic].  With all due respect to the encyclopedic knowledge of Ben, I
>> took this one with a grain of salt.  And again, Wikipedia to the rescue:
>>     
>
>   I trust my own experience a lot more than I trust a Wikipedia
> article tagged as needing more citations.  But hey, what you trust is
> up to you.  But more than either of those two, I trust the Linux
> sources, and investigation there finds there's no checksum storage or
> calculation (outside of support for the LFN hacks).  So no CRC in FAT
> filesystem.
>
>   Back in the bad old days of DOS, occasionally you'd get a message
> along the lines of
>
> 	Data CRC error reading drive A:
> 	Abort, Retry, Fail?
>
> trying to read that really important file you didn't have a backup of,
> so there was a CRC *somewhere*.  Perhaps it was a floppy thing?
>   

The CRC was on the disk sectors, irrespective of any file system that 
might have been in use.
This applied to hard drives as well as floppy disks and other removable 
storage such as Syquest, Zip & Jaz disks.
So, you could get a CRC error on MS-DOS FAT, Xenix, or raw data, if the 
underlying media had a CRC failure.

Decades ago, I used to work below the file system layer often.