By Jasen Baker, Storage Architect
I once heard that in communicating your opinion or differences, you should not use personal phrases, such as "you always", "you never", "every time", etc. These make broad, sweeping assumptions which seldom reflect the truth, especially when communicating differences in products. Attention to detail, such as quoting someone's name when providing a source of argument, or consolidating many options into a single unified calculation over simplify and often times mislead readers who are looking for educated facts instead of uninformed guesses.
As an example, take a look at online value calculators. There are calculators for mortgages, calculators for the national debt, ROI calculators, and even storage capacity calculators. They do their best to point you in a certain direction, to narrow down the scope of what you will be working with, but don't truly take in all the factors, hence why the infamous asterisk * exists!
In responding to a recent blog post referencing "LeftHand Capacity Calculator" crafted to demonstrate useable percentages of available capacity, it's supposed to ALWAYS, come out this way.
To quote the blog, "That's because, regardless of how small or how large your LHN SAN, it's always:"
Image "courtesy" of NetApp
There's that word again, always.
In storage, there are useable capacities that always occur. That always, is the space you lose as a result of hardware RAID, well, unless it's hardware RAID 0.
First, the HP LeftHand storage nodes can be configured in RAID 5, 6, or RAID 10, all with various useable capacities. This calculator only has RAID 5. Why choose? The reasons are many, but most common are performance, protection and capacity. You choose, it's no different with us or any other vendor solution.
Second, "Disk rightsizing", a term used to explain why that 1TB hard drive you bought only shows ~932GB useable. Why? Well, that's because the hard drive vendors view 1MB as 1000 kbytes while your Operating system views 1MB as 1024 kbytes. That extra 24 bytes adds up which is why you truly don't get the actual hard size useable (this is before formatting it with your favorite file system as well). Again, nothing specific to use or any other vendor solution.
Third, Network RAID. What is Network RAID? Network RAID is a unique feature of the HP LeftHand SAN that allows you to CHOOSE on a per volume basis how many replicated copies of your LUN / VOLUME are distributed across the SAN. What is unique about this is it's DYNAMIC. You get to choose which volumes have it and which do not. What it offers you is the ability to survive entire node failures; if your nodes are physically separated and you lose an entire physical sites, your data remains online and available.
Hardware RAID is usually a set it and forget it configuration, and it's seldom changed. Network RAID is dynamic, because you as the customer choose to turn it on or off depending on the application protection needs. With that choice, you select the use of additional capacity to protect your data in a manner superior to standard hardware RAID. They key point here is choice. You have the choice, and if you change your mind, the system is dynamic and allows you to change the level of data protection on a per volume basis as often as desired. Unfortunately, a calculator without options isn't very reflective of real life. In essence, the above calculator was missing the infamous *Your mileage may vary...
To quote our previous blog poster "Unlike NetApp's space efficiency calculator, the LHN Duplication Calculator I've designed doesn't have any input fields or buttons..."
The HP Centralized Management interface WE designed, does have buttons, and even drop-downs, allowing you to choose how your capacity is used, ALWAYS.
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Posted
06-30-2009 9:37 PM
by
CalvinZ