Hi, > -----Original Message----- > From: Flemming Frandsen [mailto:[EMAIL PROTECTED]] > Sent: Dienstag, 26. Februar 2002 08:07 > To: [EMAIL PROTECTED] > Subject: Multible disks and performance > > > Right now I have SAP DB running along with a webserver on two hardware > mirrored SCSI disks and the performance is ok, but I would > like to know > what the database would be happiest with in terms of disk setup, for > when the time comes to tune the setup for speed. > > The box is running Linux on a dual P3 with 1 GB of RAM. > > Naturally all disks ought to be mirrored and the filesystem, data and > log ought to be on seperate disks, this means a minimum config of 6 > disks: > > Files: 1 + 1 > data : 1 + 1 > log : 1 + 1 absolutely fine > > For the filesystem mirror I think the dedicated SCSI RAID controller > will do nicely. > > Now, the question is: Who is better at doing the data and log > mirroring, > the hardware (or OS) or sapdb? > Every user level software solution (including SAPDB) has to fight the overhead of an additional system call and an additional copy action. This fight you cannot win. The operating system has an advantage since the extra copy action is not needed and the system call overhead is no problem. But if the OS kernel has to setup two SCSI controllers, it will block the system bus twice. Depending on the I/O bus architecture (doubled memory transfer due to separate controllers) and the delays during programming SCSI controllers there is some time spend in the kernel, which could be used otherwise... Since mirroring is done on page based, there is no ace to play like caching on user level. My answer is therefore, if you can afford you should choose a hardware solution!
The highest performance you will get from a storage array with a big cache. This will promise you security and performance. If it is well protected against power fail, you can reach I/O times comparable with a solid state disk. Some of our customers use a SAN solution (EMC,NetApp) with up to 16GByte Cache memory redundant power supplies and dedicated I/O processors, that do mirroring as background jobs... Or look for smart disk arrays (i.e. compaq), that allow to remove disks on the fly without any reconfiguration needed. This solution is more cost effective and just puts an extra tower into your machine room... But if you do not like to spend the money on a disk array, dedicated RAID controller cards are next choice, as you suggested. Rule of thumb: Each devspace its own disk. As more disks as better your throughput. CU jrg _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
