FW: Proposal to add a new modifier to SCSI Write commands.
Gerry_Houlder at notes.seagate.com
Mon Dec 2 17:20:53 PST 1996
* From the SCSI Reflector (scsi at symbios.com), posted by:
* Gerry Houlder <Gerry_Houlder at notes.seagate.com>
There are several postings that suggest the READ LONG/ WRITE LONG
commands aren't being supported in current SCSI devices.
I see a need for the READ LONG, WRITE LONG functions in testing. Most
major OEM accounts use these commands during drive qualification tests,
so the commands must be there. Drive vendors use this capability during
in-house testing. If a standard command weren't available, we'd have to
create a vendor unique command for this purpose. These commands are
present in all "full featured" drives that are out there.
It is true that various vendors are
making "minimal" drives to reduce costs. Reducing the EEPROM size
requires eliminating certain drive features, and the ones that aren't used
in normal systems operation are the first to go. These drives cut a lot more
features than just READ LONG and WRITE LONG to get the code size
small enough, so I suspect there are other lost features than this one that
will make these drives unattractive to many systems. In summary, these
commands won't go away unless you tell your drive vendor that low cost
is more important than supporting these commands.
I saw a complaint that few RAID controllers support these commands. I'll
bet the disk drives behind that controller support these commands, so
this isn't a disk drive issue. Can a RAID box "pass through" a READ LONG
or WRITE LONG command directly to a drive? These commands may not
be applicable at the RAID box level depending on how a redundancy
group is configured. Its possible RAID box vendors think that the ability to
physically power off a drive is their equivalent to supporting READ LONG,
WRITE LONG so they don't need them. If you need this feature, tell the
RAID box vendors. But don't use lack of support by the RAID box vendors
as evidence that disk drives are going to (or even want to) drop their
The same goes for CD-ROM industry. If you think READ LONG, WRITE
LONG are needed on re-writable drives, you need to tell these vendors.
They tend to be different companies than the disk drive or RAID box
vendors so they may not understand the need for these commands.
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