Re: [gentoo-user] Re: QEMU on a partition
On 03/03/2018 05:54 AM, Mick wrote: UDP encapsulation as used for e.g. VPN does not suffer with the same problem because it does not use the same transmission quality control mechanism as TCP. I think it's fair to say that it doesn't suffer at the protocol (TCP / UDP) level. There is nothing to prevent higher application layer retransmissions from compounding things. I am not sure if block device I/O protocols suffer the same problem - I don't really know how the read/write SCSI commands are queued and processed between host and guest OS. What I have noticed is abstraction layers relating to partitioning schemes, e.g. good ol' primary Vs logical partitions, make a difference *only* when the partition is initially mounted, but not thereafter. I've always operated under the assumption that there was additional logic ~> complexity, thus it must be slightly slower. That being said, I've long held that the performance overhead is extremely likely negligible and can be ignored. At least unless you are trying to squeeze every bit of performance out of something. I.e. HPC or low power / low speed devices. -- Grant. . . . unix || die
Re: [gentoo-user] Re: QEMU on a partition
On Saturday, 3 March 2018 03:09:25 GMT Ian Zimmerman wrote: > On 2018-03-02 20:12, R0b0t1 wrote: > > I can't find it again, but there was a neat writeup investigating the > > TCP over TCP "tunnel collapse" phenomena. When two layers are doing > > the same thing, there is a tendency for both to behave poorly. I'm not > > sure any deeper explanation was or can be offered, but it is something > > that holds true not only for network traffic, but disk IO and > > databases as well. > > I think I've seen that too, and it was when I decided to install and > learn openvpn in place of the everything-over-ssh setup I had before. I think the problem you mention refers to TCP retransmission timeouts, when you stack one TCP packet within another. RFC3439 warns against TCP layering: https://tools.ietf.org/html/rfc3439#page-7 UDP encapsulation as used for e.g. VPN does not suffer with the same problem because it does not use the same transmission quality control mechanism as TCP. I have used SSH within IPSec VPN tunnels without retransmission problems (both with and without UDP encapsulation). I am not sure if block device I/O protocols suffer the same problem - I don't really know how the read/write SCSI commands are queued and processed between host and guest OS. What I have noticed is abstraction layers relating to partitioning schemes, e.g. good ol' primary Vs logical partitions, make a difference *only* when the partition is initially mounted, but not thereafter. -- Regards, Mick signature.asc Description: This is a digitally signed message part.
[gentoo-user] Re: QEMU on a partition
On 2018-03-02 20:12, R0b0t1 wrote: > I can't find it again, but there was a neat writeup investigating the > TCP over TCP "tunnel collapse" phenomena. When two layers are doing > the same thing, there is a tendency for both to behave poorly. I'm not > sure any deeper explanation was or can be offered, but it is something > that holds true not only for network traffic, but disk IO and > databases as well. I think I've seen that too, and it was when I decided to install and learn openvpn in place of the everything-over-ssh setup I had before. -- Please don't Cc: me privately on mailing lists and Usenet, if you also post the followup to the list or newsgroup. To reply privately _only_ on Usenet and on broken lists which rewrite From, fetch the TXT record for no-use.mooo.com.
