Re: SAN vs Internal Disks

[david(at)lang(dot)hm]

On Tue, 11 Sep 2007, Decibel! wrote:

> On Tue, Sep 11, 2007 at 05:09:00PM -0400, Michael Stone wrote:
> > On Tue, Sep 11, 2007 at 03:55:51PM -0500, Decibel! wrote:
> > > Also, to reply to someone else's email... there is one big reason to use
> > > a SAN over direct storage: you can do HA that results in 0 data loss.
> > > Good SANs are engineered to be highly redundant, with multiple
> > > controllers, PSUs, etc, so that the odds of losing the SAN itself are
> > > very, very low. The same isn't true with DAS.
> >
> > You can get DAS arrays with multiple controllers, PSUs, etc.  DAS !=
> > single disk.
>
> It's still in the same chassis, though, which means if you lose memory
> or mobo you're still screwed. In a SAN setup for redundancy, there's
> very little in the way of a single point of failure; generally only the
> backplane, and because there's very little that's on there it's
> extremely rare for one to fail.

not nessasarily. direct attached doesn't mean in the same chassis, 
external drive shelves attached via SCSI are still DAS

you can even have DAS attached to a pair of machines, with the second box 
configured to mount the drives only if the first one dies.

David Lang