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Impossible rates shown in X-Center throughput alerts for shared iSCSI storage


Pete Wason

Question

I have my threshold set to 64MB/sec. Three Dell EPYC servers connected via a small 1GbE switch to a Synology FS2017 with 24x2TB SSDs in a RAID 10 config.
Currently, there are 23 VMs running on the servers - but right now it looks like only three VMs are really doing much of anything. Max disk is < 20KB/sec, max network is < 600KB/sec.

Most of the alerts look something like this:

 

Storage Throughput Alarm: The total read and write throughput of server 'manwe' on storage repository 'vmstorage' has been 95.6 MBps for the last 60 seconds.
This alarm is set to be triggered when the total throughput exceeds 64 MBps.

evendim

Nov 11, 2019 11:17 AM

 

Or, roughly 75% of the theoretical maximum rate for the switch (or, considering duplexing, close to 40%. I think). However, I also see alerts like this:

 

Storage Throughput Alarm: The total read and write throughput of server 'varda' on storage repository 'vmstorage' has been 1.9 GBps for the last 60 seconds.
Storage Throughput Alarm: The total read and write throughput of server 'varda' on storage repository 'vmstorage' has been 5 GBps for the last 60 seconds.
Storage Throughput Alarm: The total read and write throughput of server 'varda' on storage repository 'vmstorage' has been 7.2 GBps for the last 60 seconds.
Storage Throughput Alarm: The total read and write throughput of server 'manwe' on storage repository 'vmstorage' has been 9.8 GBps for the last 60 seconds.
Storage Throughput Alarm: The total read and write throughput of server 'manwe' on storage repository 'vmstorage' has been 14.2 GBps for the last 60 seconds.


You get the idea.

1. Is the server reporting incorrect rates?

2. Is X-Center misinterpreting the reported rates?
3. Is "Storage Throughput" something other than what I think it is?
4. Did I get a fantastic deal on this switch?
5. Am I dealing with Alien Technology?

Synology support confirmed that my setup is categorically incapable of such speeds.
(Disclaimer: It's really cold here. I could be doing the math wrong.)

 

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Apparently X-Center is getting that info from the iSCSI box (Synology FS2017), and it's not the speed between the box and the vhosts (which is bottlenecked by a 1GbE switch :/), it's the speed internal to the box. I've now seen "speeds" of ~40GB/sec. Synology support confirmed; it's the stuff moving around inside the box!

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