High speed continuous recording and playback for VLBI Terena 7th - - PowerPoint PPT Presentation

▶
high speed continuous recording and playback for vlbi
SMART_READER_LITE
LIVE PREVIEW

High speed continuous recording and playback for VLBI Terena 7th - - PowerPoint PPT Presentation

Mar 05, 2023 113 likes •289 views

High speed continuous recording and playback for VLBI Terena 7th TF-Storage Meeting, 2010-09-09, Poznan What is JIVE? Operate the EVN correlator and support astronomers doing VLBI. A collaboration of the major radio- astronomical research

slide-1
SLIDE 1

High speed continuous recording and playback for VLBI

Terena 7th TF-Storage Meeting, 2010-09-09, Poznan

slide-2
SLIDE 2

What is JIVE?

Operate the EVN correlator and support astronomers doing VLBI. A collaboration of the major radio- astronomical research facilities in Europe, China and South Africa NEXPReS is a three-year project aimed at further developing e-VLBI services of the EVN with the goal of incorporating e- VLBI into every astronomical EVN observation.

slide-3
SLIDE 3

Radio Astronomy

Courtesy of NRAO

slide-4
SLIDE 4

Radio vs. Optical astronomy

The imaging accuracy (resolution) of a telescope:

θ ≈ 1.2 λ/D (λ = wavelength, D = diameter)

Hubble Space Telescope: λ ≈ 600nm (visible light) D = 2.4m

θ = 0.06 arcsecond

Onsola Space Observatory: λ = 6cm (5GHz) D = 25m

θ = 600 arcseconds Wanted: 240km dish

slide-5
SLIDE 5

Very Long Baseline Interferometry

  • Create a huge radio telescope by using telescopes in

different locations around the world at the same time

  • Resolution depends on

distance between dishes and observing wavelength, milli-arc second level

  • Sensitivity on dish area,

time and bandwidth

  • Requires atomic clock

stability for timing

  • Processed in a special

purpose super-computer: Correlator, 16x 1024Mb/s

slide-6
SLIDE 6

Very Long Baseline Interferometry

  • Uses special purpose

recording machines (Mark5)

  • And special purpose packs

with 8 harddisks

  • Each telescope records at

up to 1024 Mb/s

  • 5 TB in a typical 12h
  • bserving run
  • After correlation, the

resulting dataset is a few GB

slide-7
SLIDE 7

Our current Storage System...

  • Generally 3 EVN sessions per year, 3-4 weeks each
  • The total EVN storage pool is 1.7 PB
  • Which is constantly on the move
slide-8
SLIDE 8

Very Long Baseline Interferometry

tekst

  • Initially (1990) we used

large single-reel tapes

tekst

  • Then came

harddisk-packs

  • And now: e-VLBI
slide-9
SLIDE 9

Very Long Baseline Interferometry

“Never underestimate the bandwidth of a station wagon laden with computer tapes hurtling down the highway” (Andy Tanenbaum)

Latency: 2 weeks Latency: 150 ms

slide-10
SLIDE 10

Why e-VLBI

  • Quick turn-around
  • Rapid response
  • Check data as it comes in, not weeks later

(You can’t redo just 1 telescope)

  • Logistics (disks delayed/deleted/damaged/destroyed)

Example: Cyg X-3

  • Star + black hole
  • Flares irregularly
  • Timescale: days
  • Left: 2 weeks late
  • May: Observed

flare with e-VLBI

slide-11
SLIDE 11

Last night’s e-VLBI

Obsevation of V407cyg nova outburst

slide-12
SLIDE 12

Disk VLBI e-VLBI

Full bandwidth at each station Some stations have limited connectivity Shipping takes weeks Continuous, real-time quality checks Limited by diskpool size Data never hits disk - no reruns Broken harddisks, recording problems Broken fibers, router problems Long scheduling due to logistics Target-of-Opportunity observations Better sensitivity Better reliability

Disk VLBI vs. e-VLBI

: best of both worlds

slide-13
SLIDE 13

The NEXPReS project

  • Recording at the telescope
  • Real-time transfer and recording at correlator
  • Use Bandwidth-on-Demand paths for transfer
  • Real-time correlation and quality monitoring
  • Best of both worlds: highest reliability and bandwidth
  • Shipping as much data over the network as possible
  • Higher speeds: 8 Gb/s per station, and beyond
  • Storage challenge: continuous recording at 8 Gb/s

with real-time replication and simultaneous playback

slide-14
SLIDE 14

The NEXPReS project

  • Is an Integrated Infrastructure Initiative (I3)
  • Funded under the EU Seventh Framework Programme
  • 15 Astronomical Institutions and NRENs participating
  • 4 main workpackages:
  • WP5: ‘Cloud’ correlation
  • WP6: High Bandwidth on Demand
  • WP7: Computing in a shared infrastructure
  • WP8: Provisioning High Bandwidth, High Capacity

Storage on demand

slide-15
SLIDE 15

WP8: Provisioning High Bandwidth, High Capacity Storage on demand

  • A distributed on-demand storage system:
  • Record at telescope
  • Best-effort real-time transfer
  • Record at correlator
  • Rerun once all data is complete
  • Multi Gb/s read/write performance
  • Research hardware, software, raids
  • Use for Scientific Archives (LOFAR)
  • WP coordinated by AALTO (Metsähovi, Finland)

Metsähovi Observatory

slide-16
SLIDE 16

The future of the EVN

  • More telescopes to join
  • New correlator based on FPGAs (UniBoard)
  • Higher observing bandwidths (4Gb/s, 8 Gb/s, ... )
  • NEXPReS: combined real-time and disk-based

VLBI

Uniboard New telescope in Sardinia

slide-17
SLIDE 17

Questions?