Re: ATA 4 KiB sector issues.

[Martin K. Petersen]

>>>>> "ClÃudio" == ClÃudio Martins <ctpm@xxxxxxxxxx> writes:

ClÃudio> So the question is: what are hard drive makers guaranteeing (if
ClÃudio> anything at all)?

No guarantees.  Nothing that you can get in writing, anyway.


ClÃudio> Was a 512B sector write really atomic?

Sometimes.


ClÃudio> Is a 4k one?  

Sometimes, maybe.

The problem with 4KB physical blocks is that if you do a partial or
misaligned write you'll end up having to do read-modify-write.  And that
introduces are scenario where a subsequent write error will affect
logical blocks that were not part of the I/O request.

However, you also have that with regular drives because they often write
more than the actual block undergoing I/O.  For instance to reduce
hotspot bleed to adjacent sectors.

There have been several unsuccessful attempts at nudging the drive
vendors into giving us real guarantees (supercapacitors, NVRAM or
flash-backed write cache).  No luck so far.  So people that care use
arrays with non-volatile caches.

-- 
Martin K. Petersen	Oracle Linux Engineering
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