1. Data mirrors: Techniques and IssuesBy
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 - yahoo.co.uk yahoo.co.in
High Availability - ADS mirrors
Multilingual replication -
Database Sharing –
Franchise / Local Versions -
quicken.excite.com quicken.com
Virtual Hosting - sports.catalogue.com

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

15. ERNET NOC at IUCAA

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. ftp://cdaftp.iucaa.ernet.in
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?