Hi,
I have my ESXi 5 hosts connected to my SAN SATA storage via dual 1 Gbit iSCSI network, configured with Roun-Robin Multipathing. Setup is fine all works OK. My SAN is capable of around 1000 IOPS, 400 MB/s seq. read and 250 MB/s seq. write.
Virtual machine 1: Win 2008 R2 64 bit: IOmeter, sequential write and read: got ~200 MB/s -> that's great (obviously fully utilizes 2x 1 GBit iSCSI).
Virtual machine 2: CentOS 5.7 64 bit: dd and/or bonnie++, sequential write and read: got ~80 MB/s -> that's NOT great.
All VMs configured with LSI Logic SAS. NTFS on Win and ext4 on CentOS.
I've run tests many times on different hosts (but same storage) and on many different installations of guests ... always same poor RHEL virtual disk performance. I've also run IOmeter on Win7 64 bit and got again the great ~200 MB/s.
Where's the trick? Why such slow virtual disk performace in RHEL/CentOS?