iSCSI theoretical speeds

[withanh]

My environment:
Work = 10Mbps QMOE (Qwest Metropolitan Optical Ethernet)
Home = 1.5Mpbs/896Kbps Qwest DSL
VPN connected, can ping IP's both ways
File = Windows2003SvrR2Sp2x32Disk2.iso (123,852KB)

First check was run with Ixia's QCheck monitor, it reported that work to home is 1.2Mbps and home to work is 708Kpbs. That fits with what my home DSL circuit should be showing.

Given those speeds, I should be able to download something from work theoretically at 192KBps (1536Kbps or 1.5Mbps), so a file that is 123,852KB should take 645 seconds or ~10.75 minutes. I verified that by transferring a file via FTP from work to home and it took around 15 minutes to transfer.

Please double check my math and make sure I did those conversions properly.

Now for the weirdness...
I set up a Windows based iSCSI target on a VM running at home. I used the Windows iSCSI initiator on a VM at work to connect to the iSCSI target at home over the VPN.

I then copied and pasted the same 120MB file from the VM here to the iSCSI connected drive that lives at home. It took 20 seconds for it to transfer. I verified this by connecting to my home VM and looking at the drive. Sure enough, there sat the file, I opened it and was able to view/access everything in the file.

How was this possible? Does iSCSI use some sort of voo-doo quantum mechanics magic to get the file there? It would seem to me that my file transfer speed is what it is and it should not matter if I'm transferring a file via HTTP, FTP, SCP, or across a windows share to an iSCSI target. It should only be able to move the file at it's max limit of 1.5MBps. Moving that 123,892KBps file in 20 seconds translates to 6,194KBps or 49,556Kbps (49Mbps). So how does a 1.5Mbps connection move a file at 49Mbps?

 

[RMGBELGIUM]

When the copy is finished, did you check if the disk activity dropped as well ? Because windows can say the file is there, but in background keeps on copying the rest of the data ...

NetApp Certified NCDA/NCIE-SAN

 

[withanh]

I had not checked disk activity to see, but I will do another test and watch that. I'm guessing that it is because after the 20 seconds to transfer the file I was able to open it on the other end and extract a random sample of files out of the .iso.

h

 

[TalkToQwest]

Hey there withanh, this is Brian from Qwest. I ran across your post here, and am curious if you have gotten your DSL questions/issues resolved?

If you need assistance with your Qwest DSL service, please let me know and I would be happy to help. Just e-mail me at TalkToUs@Qwest.com, with you Qwest number, and I'll look into this for you.

Thanks,
B

 

[withanh]

Hi Brian,

Thanks for posting back, that's way appreciated!

My issue isn't really so much with my Qwest DSL, I feel that my DSL is working great. It's more about iSCSI and how iSCSI works across the internet. With the DSL service I have, I should only be pulling down files at 1536Kbps (theoretical max), but on my iSCSI drive, it transferred a file at 49,556Kbps. My question is how does iSCSI transfer that fast when the connection speed is that much slower.

 

[TalkToQwest]

Ah, I see now. Well, that's impressive anyhow. :0)

Ok good, I thought that maybe there was in issue with your DSL. I am glad to here that there isn't an issue however. Just let me know if you ever do need help.

Thanks for the reply. Have a great weekend!!

B

 

[LeeMason]

It could be something to do with caching and asynchronous writes. It could be that the Windows iSCSI initiator is set for cache and async writes. How long after copying the file did you have a look at it on your home system?

I'm now sure about the Windows iSCSI initiator but are they any settings for async vs sync writes or cache sizes?


Lee Mason
Optimal Projects Ltd

http://www.opl.co.uk

http://www.backupsanywhere.com

 

[withanh]

It was literally seconds, I remoted in to look at the files.

And I didn't see anything about caching in the Windows iSCSI initiator.

Weird for sure!