SRDF is an EMC remote replication solution for business continuity and disaster recovery solution where you can have an almost real time copy of the data available at the remote site also. This remote site can be geographically located in the same area or anywhere in the world. Geographically located data centres are useful in case of a disaster.
So in a basic definition form you can say that in SRDF we will have a exact copy of the source data at the remote site and this copy will be host independent and will be taken by storage itself. Data will be replicated from the source site to remote site over the specialized networks meant for carrying heavy amount of data.
So question arises why do we need remote replication ? As discussed earlier, if a disaster happens, the data stored might get lost and the applications running on them will be down till the time we restore the situation. So to avoid this kind of situation, we needed a copy of the data from where we can restore everything. Now you might ask, why not use Tape backups or a local copy of the data in place of a remote copy. Idea behind not having only copy of the data as local is to prevent any local disaster kind of situation. While Tape backup is still a solution but should not be used as a single option for data copy, specially for highly critical applications. As we all know restoring from tape is a very time consuming process and can not be a desired solution for application which needs to be available round the clock.
SRDF logically pairs a device or a group of devices from each array and replicates data from one to the other synchronously or asynchronously. An established pair of devices can be split, so that separate hosts can access the same data independently (maybe for backup), and then be resynchronised.
Fig 1 : Typical SRDF Configuration
There are various modes of SRDF operations (Keep checking my Blog for a post on SRDF modes), out of them most popular are SRDF/S and SRDF/A .
In synchronous mode (SRDF/S), the primary array waits until the secondary array has acknowledged each write before the next write is accepted, ensuring that the replicated copy of the data is always as current as the primary. However, the latency due to propagation increases significantly with distance.
Asynchronous SRDF (SRDF/A) transfers changes made to the secondary array in units called delta sets, which are transferred at defined intervals. Although the remote copy of the data will never be as current as the primary copy, this method can replicate data over considerable distances and with reduced bandwidth requirements and minimal impact on host performance.
Other forms of SRDF integrate with clustered environments and to manage multiple SRDF pairs where replication of multiple devices must be consistent (such as with the data files and log files of a database application).
Now the question arises that how the data flows from one symmetrix box to another remote box, what replication medium does it use and how far can you replicate, will it copy instantly or it's a time taking activity, what will be RTO and RPO for this, what kind of devices can participate in SRDF operations. I will surely be posting details on these topics in my coming blogs. Till then enjoy !
Also check Various SRDF Device States
So in a basic definition form you can say that in SRDF we will have a exact copy of the source data at the remote site and this copy will be host independent and will be taken by storage itself. Data will be replicated from the source site to remote site over the specialized networks meant for carrying heavy amount of data.
So question arises why do we need remote replication ? As discussed earlier, if a disaster happens, the data stored might get lost and the applications running on them will be down till the time we restore the situation. So to avoid this kind of situation, we needed a copy of the data from where we can restore everything. Now you might ask, why not use Tape backups or a local copy of the data in place of a remote copy. Idea behind not having only copy of the data as local is to prevent any local disaster kind of situation. While Tape backup is still a solution but should not be used as a single option for data copy, specially for highly critical applications. As we all know restoring from tape is a very time consuming process and can not be a desired solution for application which needs to be available round the clock.
SRDF logically pairs a device or a group of devices from each array and replicates data from one to the other synchronously or asynchronously. An established pair of devices can be split, so that separate hosts can access the same data independently (maybe for backup), and then be resynchronised.
There are various modes of SRDF operations (Keep checking my Blog for a post on SRDF modes), out of them most popular are SRDF/S and SRDF/A .
In synchronous mode (SRDF/S), the primary array waits until the secondary array has acknowledged each write before the next write is accepted, ensuring that the replicated copy of the data is always as current as the primary. However, the latency due to propagation increases significantly with distance.
Asynchronous SRDF (SRDF/A) transfers changes made to the secondary array in units called delta sets, which are transferred at defined intervals. Although the remote copy of the data will never be as current as the primary copy, this method can replicate data over considerable distances and with reduced bandwidth requirements and minimal impact on host performance.
Other forms of SRDF integrate with clustered environments and to manage multiple SRDF pairs where replication of multiple devices must be consistent (such as with the data files and log files of a database application).
Now the question arises that how the data flows from one symmetrix box to another remote box, what replication medium does it use and how far can you replicate, will it copy instantly or it's a time taking activity, what will be RTO and RPO for this, what kind of devices can participate in SRDF operations. I will surely be posting details on these topics in my coming blogs. Till then enjoy !
Also check Various SRDF Device States
Disaster recovery plan is the most important thing for any business in 2016. Everything is made online, even if you are an artist you probably pass your payments, tax and more by a computer. The worst thing will be losing your business record and history in one downtime!
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