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Re: [Xen-users] xen 3.3 -> tap:aio performance over nfs
- To: C V <rayvittal-lists@xxxxxxxxx>
- From: Jia Rao <rickenrao@xxxxxxxxx>
- Date: Fri, 30 Jan 2009 23:25:05 -0500
- Cc: xen-users@xxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 30 Jan 2009 20:26:07 -0800
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I am mounting file-based disk images (tap:aio) ) for VM from a nfs server (SATA, RAID 5) too. The link to the nfs server is a 1 G ethernet.
The read and write performance is also bad, all around 10M/s. The write size for the nfs client is set to 8K (I tested with different sizes, like 16K and 32K, similar performance).
Is there any way to optimize the disk-based VM performance? Currently there are 10+ VMs mounted to the nfs server and they include webservers, OLTP, and Java application servers.
Thanks.
On Fri, Jan 30, 2009 at 9:04 PM, C V <rayvittal-lists@xxxxxxxxx> wrote:
I've been getting disappointing performance for file-backed disks mounted using tap:aio over an NFS mount.
For example, bonnie++ reports 3 MB/s for block writes in the domU to
that
disk, but in dom0, bonnie++ reports 38 MB/s for that same mount. The
same domU can get 40 MB/s to the same filer using a phy: block device
over iSCSI .
It seems that
1. tap:aio causes synchronous writes to the nfs mount (6 writes, wait for ack, write 6 more etc) as opposed to NFSv3 async write
2. Each synchronous write writes very small blocks (4K bytes vs max of 32K bytes)
Is there any configuration option to tweak this behavior to get better-performing async writes to the filer?
Thanks
--
CV
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