RemoteSHADOW FAQs-Data Replication Data Recovery

  1. How does RemoteSHADOW transport data to my site?

  2. When should we use RemoteSHADOW's Asynchronous Mode?

  3. How do you know how much bandwidth you will need?

  4. What happens if the Network fails during production?

  5. In what operating environments is RemoteSHADOW supported?

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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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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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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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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In what operating environments is RemoteSHADOW supported?

RemoteSHADOW was first introduced on Compaq Corporations ( Digital Equipment Corporations) VAX and Alpha Systems running OpenVMS.

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