Re: impact of 4k sector size on the IO & FS stack

[Ric Wheeler <ric@emc.com>]

Jeff Garzik wrote:
> Alan Cox wrote:
>> I would be interested to know what the disk vendors intend to use as
>> their strategy when (with ATA) they have a 512 byte write from an older
>> file system/setup into a 4K block. The case where errors magically 
>> appear
>
> Well, you have logical and physical sector size changes.
>
> First generation of 1K sector drives will continue to use the same 
> 512-byte ATA sector size you are familiar with.  A single 512-byte 
> write will cause the drive to perform a read-modify-write cycle.  This 
> configuration is physical 1K sector, logical 512b sector.
It would seem that most writes would avoid this - hopefully the drive 
firmware could use the write cache to coalesce contiguous IO's into 1k 
multiples when getting streams of 512 byte write requests.
>
> A future configuration will change the logical ATA interface away from 
> 512-byte sectors to 1K or 4K.  Here, it is impossible to read a 
> quantity smaller than 1K or 4K, whatever the sector size is.
>
>     Jeff
I will try and see if I can get some specific information on when the 
various flavors of this are going to appear...

ric