Comment 154 for bug 595047

I have really noticed this lately.

I replace a old server running and older kernel. The replacement hardware was by orders of magnitude more powerful. The I/O system in the old machine was a 4 disk hardware RAID 5 on 64 bit PCI with the very first SATA 10,000RPM WD Raptors (WD740-00FLA). The new machine has and 8 disk hardware RAID 5 using the new 300gig 10,000rpm Velociraptor SATA drives on PCI-Express. The old machine had a Pentium 4 HT CPU. The new machine has a 4 core Core 2 CPU. All high end gear.

The new machine does get far better disk through put, however on the workloads the latencies seem far higher, the interactvity of the machine is poor and all CPU core show high I/O waits.

This machine serves a application that run from Samba shares to 15 or so Windows workstations. This involved lots of file activity on large flat file database files. Some of the files are up to 4GB in size.

The old server was very busy however not a huge amounts of I/O wait was seen. On the new server using a 2.6.18 kernel on an enterprise distro the I/O waits are heaps higher. Especially noticed at backup times. Users of the system have noticed the extra latencies when the system is busy and at these time the I/O waits are high.

The server feels slower than the old machine and this should not be so.

Just thought I would let you know this info as it seems a hard to quantify this to real world.