[clug] OT: newbie RAID question

Carlo Hamalainen carlo.hamalainen at gmail.com
Fri Jun 18 19:48:01 MDT 2010

On Fri, Jun 4, 2010 at 10:29 AM, Michael Cohen <scudette at gmail.com> wrote:
> Yes they will. In a 3 disk RAID5 one disk is used for parity and two
> for data. The parity is usually rotated through the disks. They will
> see half the data for the blocks that dont have parity. Even with
> parity if one of the other disks is all 0 they will see the data
> (because parity of one block with data and one block with 0 is the
> data again - simple xor operation).

Doesn't RAID5 distribute the parity blocks across all disks in the array?

Anyway after much wrangling I got a cheap SAS controller card and
tried PhotoRec. Recovering large files (eg. complete spreadsheets) was
a bit of a fail but I did get lots of sensitive data off the drive
because PhotoRec looks for sequences of ASCII characters, and some of
our daily uploads are done using plain text files. Details here:


Carlo Hamalainen

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