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23.3. I/O Standards
This section describes I/O standards used by ATA and SCSI devices.
ATA devices must report appropriate information via the
IDENTIFY DEVICEcommand. ATA devices only report I/O parameters for
alignment_offset. The additional I/O hints are outside the scope of the ATA Command Set.
I/O parameters support in Red Hat Enterprise Linux 7 requires at least version 3 of the SCSI Primary Commands (SPC-3) protocol. The kernel will only send an extended inquiry (which gains access to the
BLOCK LIMITS VPDpage) and
READ CAPACITY(16)command to devices which claim compliance with SPC-3.
READ CAPACITY(16)command provides the block sizes and alignment offset:
LOGICAL BLOCK LENGTH IN BYTESis used to derive
LOGICAL BLOCKS PER PHYSICAL BLOCK EXPONENTis used to derive
LOWEST ALIGNED LOGICAL BLOCK ADDRESSis used to derive:
BLOCK LIMITS VPDpage (
0xb0) provides the I/O hints. It also uses
OPTIMAL TRANSFER LENGTH GRANULARITYand
OPTIMAL TRANSFER LENGTHto derive:
sg3_utilspackage provides the
sg_inqutility, which can be used to access the
BLOCK LIMITS VPDpage. To do so, run:
sg_inq -p 0xb0 disk