Guest OS get only 40% of the disk I/O speed as on the physically server

[sfresher]

I have been running VMware ESXi on two types of servers, and they both the same problem: slow disk I/O on the guest OS.

Both types of servers are configured using local Serial SCSI RAID or SATA drive. They have either PERC 6/i SAS RAID Controller with 256MB cache or intel 82801IR Integrated

Serial ATA Host Controller. On guest Windows XP system, the average read or write speed I get is 20 MB/s; in contrast, the speed I get directly on the physically servers tops to 50 MB/s.

I have made sure that only 1 VM is up and running on the hosts when I was testing, and the suffient CPU and memeory is allocated for that VM also. Can any people suggest what's the problem?

[mphilli7823]

I have the exact same PERC controller running in a Poweredge 1900. The underlying disks of my rig are 5 1.5TB 7200 RPM drives running Raid 5. I'm attaching a benchmark screen shot of one of my Windows XP guests. The program I used to generate the benchmark is called ATTO. My I/O seems fine, but for an apples to apples comparison what utility are you using to test your I/O?

Also what is the underlying disk subsystem you are using and the layout used inlcuding Raid levels and virtual disk config?

[J1mbo]

Out of interest what is the spec of the server and the guest?

I would suggest benchmarking the storage using IOMeter on an XP/2k3 guest with 1vCPU and 1GB RAM, using a 4GB test file and running,

- 32K sequential read (read MB/s)

- 32K sequential write (write MB/s)

- 8K 0% sequential 70% read (workload IOPS)

Running the tests with 32 IO's outstanding should give about the max throughput.