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KurianOfBorg
Contributor
Contributor

Slow disk speed with Adaptec RAID card.

I have a 6 disk RAID6 array on my Adaptec 6805 with the AFM600 flash module for cache protection. All the HDDs' firmware have been upgraded and the RAID card is also running the latest firmware and drivers on ESXi 5.1.

On a native Windows installation I get over 750MB/s sustained speeds. Inside a VM I only get 250MB/s in both a VMDK as well as RDM mode. In fact, even when I unplug a disk and degrade the array, there is no reduction in performance from the 250MB/s.

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muddin
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Contributor

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taylorb
Hot Shot
Hot Shot

What virtual SCSI adapter type are you using in your VM?   SAS or Paravirtual will perform better.

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KurianOfBorg
Contributor
Contributor

I'm using the paravirtual adapter for all disks in the VM including the boot disk. The boot disk's VMDK is on an SSD. The second disk which I'm trying to benchmark is the RAID array in RDM mode, also attached to a paravirtual adapter.

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