Re: Are linux-fs's drive-fault-tolerant by concept?

[John Bradford]

> > Name an IDE or SCSI disk on sale today that doesn't retry on write
> > failiure.  Forget I said 'Generally do'.
> 
> I don't know about drives currently on sale, but I think
> it is possible that some Flash or DRAM-based IDE pseudo-disks
> do not have extensive sector remapping features. They can just
> do ECC thing and error out.

Flash devices generally have wear-leveling, so I assume that they must
be doing some extensive sector remapping all the time.  I could be
wrong on that account, though.

> Also if disk just runs out of spare sectors, it has no other
> option other than just report failure, right? (Oh,
> of course it can decide to execute 'my firmware is buggy'
> option instead ;)

Yeah, but if a device which is intellegent about bad-block remapping
actually runs out of spare sectors, that's a different failiure that
having a single defective sector.  In a server, it would definitely be
time to replace it.

> But.
> 
> The disk, which I hold in my hand *right now*, namely:
> 	WD Caviar 21200
> MDL: WDAC21200-00H
> P/N: 99-004211-000
> CCC: E3 2 APR 97 S
> DCM: AFAAYAW
> WD S/N: WT342 251 1943
> 
> does have some bad sectors and otherwise performs satisfactorily.

OK.

> It's my 'big diskette'.

[snip]

Then why don't we invent a new filesystem, for known potentially
faulty media, which handles this case - why bloat all the existing
filesystems with code to handle it?  That idea isn't that far away
from the extra layer I suggested a few posts ago, and achieves the
same sort of thing.

John.