RemoteSHADOW® FAQs:
- How does RemoteSHADOW
transport data to my site?
- When should we use RemoteSHADOW's
Asynchronous Mode?
- How do you know how
much bandwidth you will need?
- What happens if the
Network fails during production?
- In what operating environments
is RemoteSHADOW supported?
1. How does RemoteSHADOW transport data to my site?
RemoteSHADOW provides two highly reliable methods of transmitting data to a remote
site or system. With Synchronous communication your data is first written at the
production system and then sent to the remote site to be written to a remote device
for later use. Once it has been written to the remote shadow member it will be acknowledged
back to your production system so your application can continue and you can be assured
of the highest level of protection and integrity. However to ensure that production
continues with minimal performance impact there needs to be sufficient bandwidth
to continuously write I/O's at the remote site and to receive a positive acknowledgement
back at the primary system. When the number of write I/O's exceed the networks ability
to receive a timely acknowledgement from the remote system the production application
is forced to slow down and wait. This situation, which can be caused by large amounts
of write I/O's and/or insufficient bandwidth is generally unacceptable as the daily
production systems are adversely affected and therefore needs to be avoided whenever
possible.
When your application experiences an unusually high activity level that generates
an unexpected increase write I/O's, RemoteSHADOW unique Asynchronous communication
feature can continue to ensure continuous availability, integrity and no production
system slowdowns without increasing bandwidth or costs.
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2. When should we use RemoteSHADOW's Asynchronous Mode?
When your daily write I/O's have sustained peak periods that are very high on a
comparative basis to the rest of your computational day then our Asynchronous Mode
is ideal to help you manage the peak periods while ensuring that data is written
in the order the I/O's were originally issued. Or if you can't afford to pay the
high cost of bandwidth to deal with peak periods or latency delays caused by transfers
over great distances then Asynchronous communication is the answer!
RemoteSHADOW Asynchronous feature always works to stay fully synchronized with the
production systems. However during peak periods, either expected or unexpected,
RemoteSHADOW manages the "peaks" by ensuring that the write I/O's are applied at
the local side and then sent in time ordered sequence to the remote side. These
I/O's are written within a latency period, measured in seconds, that you decide
your business can "tolerate" during RemoteSHADOW's installation and modified on
an as needed basis, even during the production day. RemoteSHADOW will queue these
I/O's and apply them as bandwidth becomes available and within your specified time
limit.
With RemoteSHADOW's Asynchronous Communication method you can buy less bandwidth,
maintaining your ability to continue computing operations in the event of a primary
site failure.
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3. How do you know how much bandwidth you will need?
RemoteSHADOW comes with an advanced Data Collection Program that can be installed
on your system(s) to measure the write I/O traffic generated for each disk device
during a typical day(s). It will then provide a bandwidth model that suggests the
appropriate bandwidth that would allow you to select the optimal choice of synchronization
and bandwidth expense that your business and budget allow.
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4. What happens if the Network fails during production?
RemoteSHADOW's Network Restart facility was designed to protect against the all
too familiar "transient network failure." Too often when networks are interrupted
it causes other replication products to fail out the remote site or cause a split
or partitioned environment. Very often these network failures are for short or relatively
short periods of time. Nonetheless they can cause replicated systems to initiate
unnecessary and lengthy network copies. During these times your business is unnecessarily
exposed to a site failure as the information is no longer consistent as the copy
is performed. RemoteSHADOW avoids this problem and our customers will back us up!
RemoteSHADOW Network Restart feature tolerates these interruptions by queuing them
in time ordered sequence at the local site and then after restarting your network
it will "drain" the backlogged write I/O's by applying them and any current I/O's
in an orderly fashion. RemoteSHADOW's Network Restart feature makes the implementation
of disaster recovery even easier for your system!
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5. In what operating environments is RemoteSHADOW supported?
RemoteSHADOW was first introduced on Compaq Corporations ( Digital Equipment Corporations)
VAX and Alpha Systems running OpenVMS. In 1998 Advanced Systems Concepts announced
that RemoteSHADOW was available for Tru64 UNIX* systems.
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