On Sun, Mar 4, 2012 at 6:06 PM, Pandu Poluan <[email protected]> wrote:
>
> On Mar 5, 2012 4:59 AM, "Grant" <[email protected]> wrote:
>>
>>
>> All my drives says this from fdisk:
>>
>> Units = sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>
>> So it doesn't matter where the first partition starts?
>>
>
> Older BIOSes don't understand that hard disks now can have 4KiB sectors, so
> some of the "advanced format" hard disks report a sector size of 512B. But
> behind the scenes, the hard disk maps the logical sector to a subsector of
> the physical sector.
>
> The only sure fire way to find out if your hard disk uses 4KiB sectors is to
> open your computer and eyeball the hard disk. All 4KiB hard disks that I
> know of have statements on their surface that tell me so.
>
> Rgds,
I think I must be kind of late to this conversation, but as background
consider hdparm -i coupled with Google for the actual spec:
c2stable ~ # hdparm -i /dev/sdg
/dev/sdg:
Model=WDC WD10EARS-00Z5B1, FwRev=80.00A80, SerialNo=WD-WCAVU0415076
Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=50
BuffType=unknown, BuffSize=unknown, MaxMultSect=16, MultSect=off
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6
AdvancedPM=no WriteCache=enabled
Drive conforms to: Unspecified: ATA/ATAPI-1,2,3,4,5,6,7
* signifies the current active mode
c2stable ~ #
With the model number it takes only a minute to determine that this WD
drive is a 4K sector drive. (Which is marked on the drive, as you
state, but I'd have to remove it to find that out.)
Now, in terms of performance, the only requirement (as I understand
it) is that all drive partition be aligned to sector addresses
divisible by 8. (512 * 8 = 4K) The reason 63 gives low performance is
because it's not naturally aligned by 8. With older versions of fdisk
if I started the first partition at 64 then the performance was fine
and only one sector was wasted.
M$, for whatever reason, decided to start at 2048, which is divisible
by 8, reserving the area at the front of the drive for (I think) their
boot loader and other M$-y things. My understanding of why fdisk now
enforces this is simply to be more careful about not overwriting the
M$ boot loaderif it's there. (But I could be very wrong about that!)
Remember, it's possible to make a dual boot system using M$'s loader
instead of grub, and important that fdisk doesn't mangle it when
someone is using that tool.
Just my views,
Mark
