perfSONAR User Q&A and Other Discussion

[Hyojoon Kim <>]

Most of what you experienced is probably related to the continuous, linear, all-output nature of the logging being done by the system.  It will run well until the unused RAM commandeered by the kernel fills.  Then it gets turned int a big FIFO constrained by the rate the card can ingest the old pages as they’re written out.  Couple that with the tendency of flash devices to slow down as they wear and you’ll eventually end up with a system that doesn’t perform well.

Yes, this seems to summarize the explanation of the cause well!

Logging to RAM is a good choice if you’ve got it to spare and don’t mind losing it if the system dies, but shipping it across the network to a logging server with magnetic storage is better.

Yes, we also discussed about this. My only concern was: would transmitting continuous logs through the interface that also does the continuous owamp influence the measurement results? I guess it depends on how much log is sent, including the size. Maybe the effect is negligible. I’m not sure myself, but yes, definitely also a good idea worth a try.

The only good, non-magnetic solution for keeping it on the system is to use devices with single-level-cell (SLC) flash instead of the multi-level-cell (MLC) you find in products aimed at the consumer market.  MLC wins out on density and cost per bit, but SLC does better on speed, durability and, if you care about it, power consumption.  Sadly, SLC is unbelievably expensive and doesn’t do much to further the cause of inexpensive perfSONAR nodes.  The 3D XPoint memory that Intel and Micron announced this spring will alleviate those problems, but I wouldn’t expect to see it in SD cards for another year to 18 months.

Oh wow, good in-depth information to know. Thanks for this! 

Regards,

Joon