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There are always limits, aren't there? It's always dangerous to say that "no one will ever need that much ( disk drive, ram, processor speed or whatever) but terabyte drives really would seem to be beyond anything I can imagine for most folks. Gosh, it took me several years to fill a 30GB drive..

Well, if you ever need it..

From: Bela Lubkin <filbo@armory.com>
Subject: IDE drives up to 1, maybe 2 terabytes ought to work
Date: 17 Nov 2005 05:53:47 -0500
Message-ID: <200511170253.aa11628@deepthought.armory.com> 

Just an FYI...

In past discussions I've mentioned that the latest versions of the OSR5
"wd" IDE driver are supposed to support drives up to 2 terabytes.  I
also mentioned that this capability had never been properly tested.


Well, it still hasn't been _properly_ tested since there is no such
thing as a 2TB IDE drive this year.  But I have successfully tested one
of the two most crucial code paths.

Successful 2TB support will require three things.

First, the HBA driver must attempt to support it.  As far as I know,
only "wd" does so today.

Second, the kernel and utilities must be able to deal with sectors/track
values larger than 63.  "wd" uses 63 sectors for drives up to about
1/2TB, 127 up to 1TB, and 255 up to 2TB.  (Other HBA drivers, if they
were modified to try to support 2TB, might make different choices about
boundaries.)  [I can perform the necessary modifications to HBA drivers,
if any manufacturers are reading this...]

Third, the kernel and utilities must be able to deal with absolute
sector numbers larger than 2^31.  Sector numbers are stored in the
kernel data type `daddr_t', which is defined as a signed 32-bit integer.
This could easily cause problems at the 1TB boundary.

I recently realized that I could test the sectors/track issue without
any sort of large drive.  All I needed to do was force a small drive to
a large geometry.


So I faked up a 1GB drive with 32 cylinders, 255 heads and 255
sectors/track.  Filled it with data, booted from it, fsck'd it, etc.,
all was fine.

This shouldn't be taken as a thorough test, but there's no real reason
to expect lurking trouble.

Based on my tests, IDE drives up to 1TeB (1.099TB in drive manufacturer
measurements) should work.

It remains to be seen whether daddr_t's signed definition will be a
problem.  I have some hope that it will be OK.  That is the only
remaining barrier to IDE drives up to 2TeB.

OSR5 won't be able to handle any kind of drive larger than 2TeB.  (If
the controller makes it look like multiple 2TeB drives, they will work.)

None of this relates to OSR6 in any way.  I don't know what the limits
are on OSR6.

>Bela<

2005-11-17: I am looking for an interesting job that takes advantage of
            my skills.  Resume at <http://lubkin.com/bela/resume.html>.
 

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