Döhr, Markus ICC-H wrote:
Hello again!
>>One of our customers is running a largish (6 GB and growing)
>>MaxDB 7.5 (on Linux) instance on standard server hardware.
>>The installation suffers from the MaxDB "feature" of slow
>>index/table scans (about 900 kbyte/s on this machine with
>>disks that could deliver 40MB/s).
>>
>>They are about to install a HP EVA 4000 SAN which we could
>>connect to with a Fibre Channel link.
>>
>>The question is: Will this improve performance "out of the
>>box"? Is such a SAN something MaxDB can be tuned for? I've
>>heard rumors that there is hardware the DB doesnt read that
>>slowly from. Does anyone here have experience with this?
>
>
> HP 4000 is the successor of HP 3000 on which we are running all our SAP
> applications.
>
> Performance is faster than with direct attached SCSI, no doubt, but all our
> MaxDB production system don't max out the maximum throughput of the EVA.
>
> For maximum throughput it's advisable, to have the largest CACHE_SIZE
> possible. If your DB is 6 GB, I'd buy a cheap Opteron or EM64T-Box with 8 GB
> so you can put the whole database into the memory and so minimize the
> physical disc accesses.
well, the memory-approach won't work out here. Reaching 8GB is well on
the horizon, definitly this year. Main memory is not the solution here.
And even if I had enough RAM to keep only 6 GB: At the current
read-spead of the DB it takes almost 2 hours to completely slurp in the
data.
Working with this system you can actually feel this: If you access
something by an index that is currently not cached it takes _ages_ -
subsequent accesses are as quick as you would expect.
I'd like to hear something from SAP here: What kind of hardware do they
suggest for proper i/o-performance?
Raimund
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