On 7/6/2011 3:05 AM, Christoph Hellwig wrote:
> On Wed, Jul 06, 2011 at 05:22:21PM +1000, Dave Chinner wrote:
>> Unless you have a good sized chunk of BBWC in front of your disks,
>> in which case internal logs are just as fast. In fact, internal logs
>> can are often faster in this case because an internal log on a 12
>> disk RAID6 array can sink a whole log more bandwidth than an external
>> log on a 2-disk RAID0 mirror.....
>> At least, that's what my hardware tells me. ;)
> Sure, a nice BBWC setup will give you good results. But it's generally
> much more expensive than a simple setup with a raid5 or 6 and a mirror for
> the log device.
If you're talking consumer grade gear, well, sure, as there is no such
thing as a consumer hardware RAID card. In the world of branded OEM
'enterprise' gear, you can get a BBWC RAID card solution for little more
than two drives. Are most XFS admins running consumer or enterprise
LSI 9260-4i w/512MB BBWC = $485 USD
Intel RES2SV24024P expander = $280 USD
Total = $765 USD
2 HP 146GB 10kRPM SAS drives = $520 USD.
I threw in the expander as this LSI card is thoroughly limited with only
4 ports. It's also cheaper going this route than buying the sister card
with 8 ports, yet with the same performance, and 12 more total ports.