[RFC] Remove requirement of alignment to track from MBR scheme

[Warner Losh]

On May 24, 2011, at 10:35 AM, Marcel Moolenaar wrote:

> 
> On May 23, 2011, at 11:43 PM, Andriy Gapon wrote:
> 
>> on 23/05/2011 20:38 Warner Losh said the following:
>>> 
>>> On May 23, 2011, at 10:35 AM, Marcel Moolenaar wrote:
>>>> I think we've had enough rushed and ill thought-out changes going
>>>> in already and I can see that not aligning MBR partitions on a track
>>>> boundary is potentially perceived as a PITA violation.
>> 
>> _PITA_ violation? :-)
>> As to POLA - yeah, I can see people getting astonished that finally FreeBSD got
>> its sh*t together and did the right thing, years after all other OSes (even
>> Winddows) had done it.
> 
> :-)
> 
> Well, I just initialized a USB stick on my Mac and I see that it
> still adheres to some notion of geometry:
> 
> 	:
> ugen3.2: <ITE Tech Inc.> at usbus3
> umass0: <ITE Tech Inc. USB FLASH STORAGE, class 0/0, rev 2.00/2.00, addr 2> on usbus3
> da0 at umass-sim0 bus 0 scbus0 target 0 lun 0
> da0: <Simple Bonzai Xpress 2.20> Removable Direct Access SCSI-2 device 
> da0: 1.000MB/s transfers
> da0: 499MB (1023484 512 byte sectors: 64H 32S/T 499C)
> GEOM: da0s1: EBR has non empty bootcode.
> GEOM: msdosfs/MAC: EBR has non empty bootcode.
> marcelm-server% gpart show da0
> =>     32  1023424  da0  MBR  (499M)
>       32       31       - free -  (15k)
>       63  1023372    1  fat32  (499M)
>  1023435       21       - free -  (10k)

does fdisk report the same thing?  When I was poking, the 16GB stick I have reported something similar to this via gpart show, but showed there was nothing at the end when reported with fdisk.

> gpart synthesized a 64 head, 32 sectors/track geometry, which
> is not the same as the 63 sectors/track that Mac synthesized.
> Yes, this demonstrates the bogosity of geometry, but it also
> shows that it still exists.

It still exists, but on the other hand it isn't *that* useful...

> All I'm saying: be careful.

Agreed.  But the care should be on the creation side, not on the interpretation side.  In general, we should believe what the MBR says and not do the kinds of rounding we do with creation.  Also, I think that we should allow non-aligned to fake geometry creations if the user desires (or maybe even go so far as to make that the default and have alignment forcing be a requested behavior).

Warner

> -- 
> Marcel Moolenaar
> xcllnt at mac.com
> 
> 
> 
>