Snapshot 101: Copy-on-write vs Redirect-on-write

Good post by W. Curtis Preston (thank you)

There are two very different ways to create snapshots: copy-on-write and redirect-on-write. If IT is considering using the snapshot functionality of their storage system, it is essential to understand which type of snapshot it creates and the pros and cons of using either method.

Rather than the more common term volume, this column will use the term protected entity to refer to the entity being protected by a given snapshot. While it is true that the protected entity is typically a RAID volume, it is also true that some object storage systems do not use RAID. Their snapshots may be designed to protect other entities, including containers, a NAS share, etc. In this case, the protected entity may reside on a number of disk drives, but it does not reside on a volume in the RAID or LUN sense.

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Not all Snapshots are the same

Good post by George Crump (thank you)

In an upcoming webinar, Storage Switzerland will make the case for using snapshots as a primary component of data protection. For this strategy to work several things are needed from the storage infrastructure. First, it must be able to keep an almost unlimited number of snapshots; second, it needs to have a replication process that can transfer those snapshot deltas (the changed blocks of data) to a safe place; and third, the entire storage infrastructure has to be very cost effective. In this column we will look at that first requirement, the ability to create and store a large amount of snapshots without impacting performance.

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