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Data mirrors: Techniques and Issues

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1 Data mirrors: Techniques and Issues
By Sarah Ponrathnam

2 Overview Introduction… What is Data Mirroring?
Techniques of Mirroring… Motives for Mirroring… Mirror site Issues… Popular Mirroring Tools in Unix… Mirroring Experience at IUCAA…

3 What is data mirroring? Creating an exact duplicate copy in real-time.
In terms of web sites, sites are often mirrored to reduce the traffic on one server.

4 Techniques of Mirroring
Replication is one way to solve availability problem. Distributed Servers Cluster Servers Web site Mirrors

5 Techniques of Mirroring
Distributed Servers: Large web destinations such as google, Yahoo have enough capital to set up and to support distributed servers. Eg.

6 Techniques of Mirroring Cluster servers:

7 Techniques of Mirroring
Website Mirrors: Mirrors simply compare and pull the contents from a single master web site at a regular intervals and make identical contents available on another computer, ideally closer to the users making use of it.

8 Motives for Mirroring Load Balancing -
High Availability - ADS mirrors Multilingual replication - Database Sharing – Franchise / Local Versions - Virtual Hosting -

9 Mirroring Issues Maintenance of mirror-sites in different geographical locations. Integrity of the mirrored contents Providing Host-Independent URLS. Initial transfer of data Optimization Economical constraints Providing Efficient routing

10 Popular Mirroring tools on Unix
RSync Wget Mirror

11 Mirroring Experience IUCAA (Inter University Centre
For Astronomy and Astrophysics) works closely with ERNET (Educational and Research NETwork) to make this network a content oriented networkhttp://

12 ERNET India ? In 1986, then Department of Electronics
had initiated a project "ERNET" with the funding from UNDP. The objective was to establish and operate a nationwide Internet for the Indian academic and research community. Now it has become a full pledged ISP known as ERNET India.

13 ERNET partners

14 ERNET Network


16 Mirrors available in IUCAA
VizieR provides access to the most complete library of published astronomical catalogues and data tables available on line, organized in a self-documented database.

17 Mirrors available in IUCAA
The NASA Astrophysics Data System (ADS) maintains four bibliographic databases containing more than 4 million records.

18 VOI Data Archives at IUCAA
SDSS Sloan Digital Sky Survey – 1 Tb 2MASS 2 Micron All Sky Survey – 194 Gb 2dfGRS 2 degree field Galaxy Redshift Survey – 5.5 Gb 2QZ 2 Degree field QSO Survey – 630 Mb  FIRST Survey Faint Images of Radio Sky at Twenty centimeters – 226 Gb

19 VOI Hardware

20 Mirror-site under construction
Chandra Data Archive (CDA) 424 GB data is available through ftp service. Incremental update is being done regularly. Web based CDA service will be provided, once the new release of CXCDS software is made available.

21 Acknowledgement Dr. Francois Ochsenbein - VizieR
Dr. Guenther Eichhorn and Dr.Alberto Accomazzi - ADS Dr. Ramadurai Padmanabhan - CDA

22 Questions or Comments?

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