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Does the SCSI READ CAPACITY command?

Posted on 2010-09-21
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Last Modified: 2012-05-10
Does the SCSI READ CAPACITY command value of block size is the block size set the File system block size?
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Question by:areyouready344
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Ferrosti earned 63 total points
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Your filesystem does not see the SCSI protocol, so these values are independend from one another.
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by:Duncan Meyers
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http://en.wikipedia.org/wiki/SCSI_Read_Capacity_Command

Returns the block length in bytes. The block length is the block as written to the underlying device - for example, 64K for an EMC CLARiiON array, or 512 bytes for a singles disk on a SCSI controller.
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by:dlethe
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No, this is the block size for the selected physical device, which is usually 512 bytes.  The CDB has no knowledge nor does it care about the file system, or even if the disk has data or a file system on it.  This is a simple CDB that reports number of addressable blocks on selected device.

To change block size, you need to use MODE SELECT command.
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by:dlethe
dlethe earned 125 total points
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p.s. READ_CAPACITY returns both block size and # of addressable blocks, and there is both a 10-byte and 16-byte variation.  The 10-byte variation is only good for devices under the 2.09TB threshold.  16-byte variation of the command is now supported on most operating systems, but not all.
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