HP StoreOnce 4430 HP StoreOnce Backup System Concepts and Configuration Guidel - Page 83

What actually happens in replication?, Limiting replication concurrency, WAN link sizing

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between sites. In all reporting on the StoreOnce Management GUI, the throughput in MB/sec is apparent throughput - think of this at the rate at which we are apparently replicating the backup data between sites. What actually happens in replication? Assuming the seeding process is complete (seeding is when the initial data is transferred to the target device), the basic replication process works like this: 1. Source has a cartridge (VTL) or File (NAS) to replicate 2. Source sends to target a "Manifest" that is a list of all the Hash codes it wants to send to the target (the hash codes are what make up the cartridge/file/item) 3. The target replies: "I have 98% of those hash codes already - just send the 2% I don't have." 4. The source sends the 2% of hash codes the target requested. 5. The VTL or NAS replication job executes and completes. The bigger the change rate of data, the more "mismatch" there will be and the higher the volume of unique data that must be replicated over the WAN. Limiting replication concurrency In some cases it may be useful to limit the number of replication jobs that can run concurrently on either the source or target appliance. These conditions might be: 1. There is a requirement to reduce the activity on either the source or target appliance in order to allow other operations (e.g. backup/restore) to have more available disk I/O. 2. The WAN Bandwidth is too low to support the number of concurrent jobs that may be running concurrently. It is recommended that a minimum WAN bandwidth of 2Mb/sec is available per replication job. If a target device can support for example 6 concurrent jobs, then 12 Mb/s of bandwidth is required for that target appliance alone. If there are multiple target appliances, the overall requirement is even higher. So, limiting the maximum number of concurrent jobs at the target appliance will prevent the WAN bandwidth being oversubscribed with the possible result of replication failures or impact on other WAN traffic. The Maximum jobs configuration is available from the StoreOnce Management GUI on the Local Settings tab of the Replication - Configuration page. Other tabs on this page can be used to control the bandwidth throttling used for replication and the blackout windows that prevents replication from happening at certain times. WAN link sizing One of the most important aspects in ensuring that a replication will work in a specific environment is the available bandwidth between replication source and target StoreOnce systems. In most cases a WAN link will be used to transfer the data between sites unless the replication environment is all on the same campus LAN. It is recommended that the HP Sizing Tool (http://h30144.www3.hp.com/SWDSizerWeb/ default.htm) is used to identify the product and WAN link requirements because the required bandwidth is complex and depends on the following: • Amount of data in each backup • Data change per backup (deduplication ratio) • Number of StoreOnce systems replicating • Number of concurrent replication jobs from each source • Number of concurrent replication jobs to each target • Link latency (governs link efficiency) What actually happens in replication? 83

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between sites. In all reporting on the StoreOnce Management GUI, the throughput in MB/sec is
apparent throughput – think of this at the rate at which we are apparently replicating the backup
data between sites.
What actually happens in replication?
Assuming the seeding process is complete (seeding is when the initial data is transferred to the
target device), the basic replication process works like this:
1.
Source has a cartridge (VTL) or File (NAS) to replicate
2.
Source sends to target a “Manifest” that is a list of all the Hash codes it wants to send to the
target (the hash codes are what make up the cartridge/file/item)
3.
The target replies: “I have 98% of those hash codes already – just send the 2% I don’t have.”
4.
The source sends the 2% of hash codes the target requested.
5.
The VTL or NAS replication job executes and completes.
The bigger the change rate of data, the more “mismatch” there will be and the higher the volume
of unique data that must be replicated over the WAN.
Limiting replication concurrency
In some cases it may be useful to limit the number of replication jobs that can run concurrently on
either the source or target appliance. These conditions might be:
1.
There is a requirement to reduce the activity on either the source or target appliance in order
to allow other operations (e.g. backup/restore) to have more available disk I/O.
2.
The WAN Bandwidth is too low to support the number of concurrent jobs that may be running
concurrently. It is recommended that a minimum WAN bandwidth of 2Mb/sec is available
per replication job. If a target device can support for example 6 concurrent jobs, then 12
Mb/s of bandwidth is required for that target appliance alone. If there are multiple target
appliances, the overall requirement is even higher. So, limiting the maximum number of
concurrent jobs at the target appliance will prevent the WAN bandwidth being oversubscribed
with the possible result of replication failures or impact on other WAN traffic.
The Maximum jobs configuration is available from the StoreOnce Management GUI on the Local
Settings tab of the Replication – Configuration page. Other tabs on this page can be used to control
the bandwidth throttling used for replication and the blackout windows that prevents replication
from happening at certain times.
WAN link sizing
One of the most important aspects in ensuring that a replication will work in a specific environment
is the available bandwidth between replication source and target StoreOnce systems. In most cases
a WAN link will be used to transfer the data between sites unless the replication environment is
all on the same campus LAN.
It is recommended that the HP Sizing Tool (
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) is used to identify the product and WAN link requirements because the required
bandwidth is complex and depends on the following:
•
Amount of data in each backup
•
Data change per backup (deduplication ratio)
•
Number of StoreOnce systems replicating
•
Number of concurrent replication jobs from each source
•
Number of concurrent replication jobs to each target
•
Link latency (governs link efficiency)
What actually happens in replication?
83