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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An overview of the new Virtual SAN 6.2 features

Good Post by Cormac Hogan (thank you)

If you were wondering why my blogging has dropped off in recent months, wonder no more. I’ve been fully immersed in the next release of VSAN. Today VMware has just announced the launch of VSAN 6.2, the next version of VMware’s Virtual SAN product. It is almost 2.5 years since we launched the VSAN beta at VMworld 2013, and almost 2 years to the day since we officially GA’ed our first release of VSAN way back in March 2014. A lot has happened since then, with 3 distinct releases in that 2 year period (6.0, 6.1 and now 6.2). For me the product has matured significantly in that 2 year period, with 3,000 customers and lots of added features. VSAN 6.2 is the most significant release we have had since the initial launch.

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Recalculating Odds of RAID5 URE Failure

Good Post by Matt Simmons (thank you)

Alright, my normal RAID-5 caveats stand here. Pretty much every RAID level other than 0 is better than a single parity RAID, until RAID goes away. If you care about your data and speed, go with RAID-10. If you’re cheap, go with RAID-6. If you’re cheap and you’re on antique hardware, or if you just like arguing about bits, keep reading about RAID-5.

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