software replication vs hardware replication benefits or duplication

if your SAN replicates to a DR SAN at hardware level, e.g. everything, does this reduce the need to have backup software that also has a software level replication element (i.e. veeam), e.g is this duplicating the same feature of the SAN's built in replication facility, or does it offer benefits above and beyond?
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pma111Asked:
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nociSoftware EngineerCommented:
Immediate Replication never is an alternative for backups. It prevents meltdown in case of a small component failing in a bigger context.
(ie. If you have raid 1, 4, 5, 6 etc. you still need a copy be made regularly to other media).
It should be possible to have multiple targets to copy to so if a backup fails there still is a previous backup...

Replication to an off-site location can help when the building burns down. (if offsite is far enough away). Does you processing also have redundancy then?
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pma111Author Commented:
I'm not trying to argue that replication replaces backups, what I am asking is if your SAN's replicate at hardware level (hardware replication), do you still need a backup product that also does replication?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
if your SAN replicates to a DR SAN at hardware level, e.g. everything, does this reduce the need to have backup software that also has a software level replication element (i.e. veeam)

Yes, Veeam and the rest is just poor mans replication, SANs do it at the block level, and just repicate block changes, more effeciently than software!

There is no need to have both, but many do not have SAN to SAN replication, or have different SANs from different vendors, which then makes replication difficult.

SAN replication - quicker and more efficient, and more - does not rely on have a Windows VM to control or drive it, which you need to administer.
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robocatCommented:
Built-in SAN replication can be more efficient than using external software replication. But it depends on the specific SAN vendor and how sophisticated the SAN is. Because the SAN manages it's own storage, it is best placed to do more efficient block level differential transfers, block level deduplication etc...

So the question can not be answered in general. Cheap SANs may be very inefficient compared to external software.
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nociSoftware EngineerCommented:
Then there is the High Availability usecase where you run two Completely independant SANs where the server uses BOTH for each disk in a raid-1 config.  So if one SAN fails, or must go down for maintenance the systems can continue to work uninterrupted.
(As far is mirror management on the server allows, the system is then obviously the one that synchronized the lot).
A SAN-> SAN replication will not help here.
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andyalderCommented:
Bear in mind that a SAN is filesystem agnostic, if you defrag the local system all those block changes get replicated to the remote copy whic is completely unnecessary and may use up all your bandwidth. You also have to be very careful about failover/failback, I once visited a site where the old copy got replicated over the new after a power cut.
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