Re: Block-level CRC checks

Alvaro Herrera wrote:
> XFS, for example, zeroes out during recovery any block
> that was written to but not fsync'ed before a crash.  This means that if
> we change a hint bit after a checkpoing and mark the page dirty, the
> system can write the page.  Suppose we crash at this point.  On
> recovery, XFS will zero out the block, but there will be nothing with
> which to recovery it, because there's no backup block ...

Really? That would mean that you're prone to lose data if you run 
PostgreSQL on XFS, even without the CRC patch.

I doubt that's true, though. Google found this:

http://marc.info/?l=linux-xfs&m=122549156102504&w=2

See the bottom of that mail.

Although, Florian Weimer suggested earlier in this thread that IBM DTLA 
disks have exactly that problem; a sector could be zero-filled if the 
write is interrupted.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com