System information

BLKSSZG ET : l o g i cal _bl o ck_si ze
BLKIO MIN: mi ni mum_i o _si ze
BLKIO OP T : o pti mal _i o _si ze
23.3. St andards
This section describes I/O standards used by ATA and SCSI devices.
ATA
ATA devices must report appropriate information via the ID ENT IFY D EVIC E command. ATA devices
only report I/O parameters for physi cal _bl o ck_si ze, l o g i cal _bl o ck_si ze, and
al i g nment_o ffset. The additional I/O hints are outside the scope of the ATA Command Set.
SCSI
I/O parameters support in Red Hat Enterprise Linux 6 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
BLO C K LIMIT S VP D page) and R EAD C AP AC IT Y(16 ) command to devices which claim
compliance with SPC-3.
The READ C AP AC IT Y(16 ) command provides the block sizes and alignment offset:
LO G IC AL BLO C K LENG T H IN BY T ES is used to derive
/sys/bl o ck/disk/q ueue/physi cal _bl o ck_si ze
LO G IC AL BLO C KS P ER P HY SIC AL BLO C K EXP O NENT is used to derive
/sys/bl o ck/disk/q ueue/l o g i cal _bl o ck_si ze
LO WEST ALIG NED LO G IC AL BLO C K AD D R ESS is used to derive:
/sys/bl o ck/disk/al i g nment_o ffset
/sys/bl o ck/disk/partition/al i g nment_o ffset
The BLO C K LIMIT S VP D page (0 xb0 ) provides the I/O hints. It also uses O P T IMAL T R ANSFER
LENG T H G RANULAR IT Y and O P T IMAL T R ANSFER LENG T H to derive:
/sys/bl o ck/disk/q ueue/mi ni mum_i o _si ze
/sys/bl o ck/disk/q ueue/o pti mal _i o _si ze
The sg 3_uti l s package provides the sg _i nq utility, which can be used to access the BLO C K
LIMIT S VP D page. To do so, run:
# sg_inq -p 0xb0 disk
23.4 . St acking I/O Paramet ers
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