Re: Support for 4KB sectors size disk ?

[Steven Bellovin <smb%cs.columbia.edu@localhost>]

On Jan 11, 2010, at 9:55 PM, Johnny Billquist wrote:

> Thor Lancelot Simon wrote:
>> On Mon, Jan 11, 2010 at 05:21:41PM -0800, John Nemeth wrote:
>>>     Although at one time it was common to be able to format drives
>>> with different sector sizes, that was over two decades ago.  It is
>>> doubtful that any current operating system would be happy with a hard
>>> drive that had a sector size other than 512 bytes.  Thus they can't
>>> change that until current OSes become an historical footnote.
>> You're kidding, right?  Maybe, again, you should stop speaking whereof
>> you know not.
>> Just as one example (which accounts for the large number of SCSI/FC/SAS
>> disk drives one still finds on the surplus market which are formatted for
>> 524 byte sectors):
>>      
>> http://publib.boulder.ibm.com/infocenter/dsichelp/ds6000ic/index.jsp?topic=/com.ibm.storage.smric.help.doc/f2c_reformattingopensddms_1v5bpp.html
>> It may not be an operating system you use, but it's certainly still a
>> current one.
> 
> Well, technically any disk will have more than 512 bytes of data for each 
> sector. It's just that 512 bytes is what is presented to (and usable by) the 
> host system, and those disks by IBM are no different.
> They still present 512 byte sectors to the host OS. To quote the page you 
> linked to: "The data portion of the sector remains at 512-bytes for all host 
> systems."
> What underlying format is used, and what data the controller stores and uses, 
> to make sure the host is serviced with the correct, and fault free data, is 
> of little concern here. We are not, after all, making disk controllers, are 
> we?
> 
> However, the age of random block sizes for disks (exposed to the OS) is way 
> more than 2 decades back.
> 
> I'd say that would be about 4 decades ago, and maybe more.

The IBM 360 series, and its flagship operating system OS/360, circa 1965, made 
heavy use of such features.  IBM introduced its first 512-byte sector drives 
around 1979 or 1980, but they certainly didn't abandon the older style then.  I 
stopped working on mainframes some time in 1981, so I don't know what happened 
after that.
> 
> Oh, and I don't expect the 512 bytes/block paradigm to change any time soon. 
> It's probably one of those things we will live with for ever. The underlying 
> disks might start doing something else, but you'll probably still be able to 
> see, and treat the disk as if it had 512 byte blocks for as long as we live.
> 
> Just my two cents...
> 
>       Johnny
> 
> -- 
> Johnny Billquist                  || "I'm on a bus
>                                  ||  on a psychedelic trip
> email: bqt%softjar.se@localhost             ||  Reading murder books
> pdp is alive!                     ||  tryin' to stay hip" - B. Idol
> 


                --Steve Bellovin, http://www.cs.columbia.edu/~smb