Please help - adaptec 2820sa not ... RESOLVED

Ensel Sharon user at
Mon Jun 19 02:44:39 UTC 2006

On Sun, 18 Jun 2006, Eric Anderson wrote:

> > 6.1 sysinstall does in fact see both 2820sa controllers, and when I put in
> > a single 160GB sata drive, it does see that single drive and I can install
> > onto it, etc.
> > 
> > Sysinstall does _not_ see my 2.7TB raid6 array.  I suspect that if it were
> > smaller than 2TB, it would see it correctly.
> > 
> > I have a number of options with which to deal with this, all of which
> > involve either wasting money or wasting disk space.  Fantastic.
> Right - FreeBSD doesn't recognize >2TB LUNs.  You should make two LUNs, 
> and concat them or stripe them with GEOM.  Don't use the large partition 
> for the OS either.
> You shouldn't waste either disk space or money.

Let's say I have 8 disks.

Let's say I require raid6.

If I make one array, I lose 25% to raid overhead.

If I make two arrays, I lose 50% to raid overhead.

So it would seem that my inability to use a >2TB LUN does indeed lose me
both space and waste money.

My solution is to use two disks as a mirror, and use the other six for a
raid6 array, thus losing 3/8 to raid overhead instead of 4/8, but it's
still worse than 2/8 which is what I wanted to do ...

Perhaps I misunderstand you ?

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