Jeffrey W. Baker wrote:
On Tue, 2006-01-31 at 09:00 -0800, Luke Lonergan wrote:
Jim,
On 1/30/06 12:25 PM, "Jim C. Nasby" <jnasby@xxxxxxxxxxxxx> wrote:
Why divide by 2? A good raid controller should be able to send read
requests to both drives out of the mirrored set to fully utilize the
bandwidth. Of course, that probably won't come into play unless the OS
decides that it's going to read-ahead fairly large chunks of the table
at a time...
I've not seen one that does, nor would it work in the general case IMO. In
RAID1 writes are duplicated and reads come from one of the copies. You
could alternate read service requests to minimize rotational latency, but
you can't improve bandwidth.
Then you've not seen Linux. Linux does balanced reads on software
mirrors. I'm not sure why you think this can't improve bandwidth. It
does improve streaming bandwidth as long as the platter STR is more than
the bus STR.
FYI: so does the Solaris Volume Manager (by default) on Solaris. One
can choose alternate access methods like "First" (if the other mirrors
are slower than the first) or "Geometric". It's been doing this for a
good 10 years now (back when it was called DiskSuite), so it's nothing new.
-- Alan
