more info on sil.c's magic number

[James Olson]

I believe I have figured out what the magic number defined in sil.h as
	uint32_t	magic;			/* 0x60 - 0x63 */
#define	SIL_MAGIC	0x2F000000

It is part of the table returned by the IDE/ATA Identify Drive information command.  Specifically,
 60h	WORD	able to do doubleword transfers if nonzero
 62h	WORD	capabilities (see #P0518)
Bitfields for IDE capabilities:
Bit(s)	Description	(Table P0518)
 13	Standby Timer values used according to ATA standard
 11	IORDY supported
 10	device can disable use of IORDY
 9	LBA mode supported
 8	DMA supported

So it seems that is why on my 2 older drives the metadata was not detected, they are so old that they don't have the 2Fh in offset 0x63 of the identify data.  Of my 3 older drives, one of them has 0Bh and the other 0Fh, and the drive that was detected had 2Fh. Apparently sil metadata is really the IDE/ATA Identify Drive information with some raid information added to the vendor specific fields.

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