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Re: AW: RAID greater than 2TB on Fedora Core 3



Masopust Christian wrote:

Hi Rick,


is it really (nowadays??) a problem of SCSI-controler?

No, it's the SCSI protocol. SCSI allows 4 bytes (32 bits) to specify the block number on a device, or 4,394,957,296 blocks. Given that most disks use a 512-byte block, that's:

4,394,957,269 * 512 = 2,199,023,255,552 bytes

or 2TB.  And before people jump on me, it's an unsigned 4-byte block
number.  A signed value would make no sense--how do you access a
negative block number?  I hear that the latest SCSI spec addresses this,
but I have no idea when (or if) it will be released and how long the
manufacturers will take to implement the new spec (if ever).

As an aside, the old 2GB file size limit was caused by using a signed
32-bit value as the second parameter in an lseek() (2^31 is
2,147,483,648, and that's in bytes--not blocks and it was signed to
allow you to seek backwards from the current postition).
----------------------------------------------------------------------
- Rick Stevens, Senior Systems Engineer     rstevens vitalstream com -
- VitalStream, Inc.                       http://www.vitalstream.com -
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