Awful FreeBSD 9 block IO performance in KVM

[Richard Yao]

On 07/21/2012 04:15 AM, Wojciech Puchar wrote:
>> da0: <QEMU QEMU HARDDISK 1.1.> Fixed Direct Access SCSI-5 device
>> da0: 3.300MB/s transfers
>> da0: Command Queueing enabled
>> da0: 409600MB (838860800 512 byte sectors: 255H 63S/T 52216C)
>>
>> It does not explain why virtio is slow though, although I still need to
>> test virtio against the latest code. I will do ivan's raw block test
>> against virtio-blk, mainly because there is no point in doing it against
>> a device whose transfers have been capped to 3.3MB/sec.
> are you sure it is really capped?
> i am not. just emulated sym device reports low speed.
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You are right. It is not capped at that speed:

root at freebsd:/root # dd if=/dev/zero of=/dev/da1 bs=16384 count=262144



262144+0 records in
262144+0 records out
4294967296 bytes transferred in 615.840721 secs (6974153 bytes/sec)

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