All of this is handled in hardware by the s/390 IO subsystem. The OS doesn't get involved at all. And if you're using array dasd such as SHARK or ICEBERG, you get RAID(5) automatically. In fact, LVM striping actually decreases performance with no additional benefit on these devices.
"You do not need a parachute to skydive. You only need a parachute to skydive twice." -Motto of the Darwin Society Gordon W. Wolfe, Ph.D. (425) 865-5940 VM Technical Services, The Boeing Company > ---------- > From: Michael MacIsaac > Reply To: Linux on 390 Port > Sent: Thursday, May 16, 2002 8:42 AM > To: [EMAIL PROTECTED] > Subject: Re: Multipath I/O on 390 Linux > > > the OS doesn't need to know about the multiple paths > > For high availability, yes. But for performance, I was *under the > impression* that Linux needs to be fooled into using the multiple > paths (haven't been able to confirm this with end-to-end performance > tests). This is done by LVM or raid-tools striping (RAID 0). *As I > understand it* the "fooling" works as follows - when a striped > volume is detected, the Linux kernel will continue with data > transfers before the previous one finishes. Then the multiple > I/O paths to the DASD will be utilized. Actually the first time > I tried a performance test, I saw a small performance gain, but it > was negligible enough to be noise. > > The recently I noticed in make menuconfig the setting: > Multi-device support (RAID and LVM) ---> > <M> Multipath I/O support > > which is not always on. So I'm hopeful for some serious performance > gains using RAID 0 and a kernel with this setting on. Any comments > from performance guys with a better background on this? > > -Mike MacIsaac, IBM [EMAIL PROTECTED] (845) 433-7061 > >
