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Mixing sizes of hard drives

josh

josh

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Question for our dealers or more technical Kaleidescape gurus:

Back in the 5U days, before there were hot-spare drives, I understood the basics of drive-size mixing: add anything less than three of a larger size drive and you won't yet get the benefit of the extra space given the RAID redundancy allocation; they'll appear as if they're the smallest-size drives until there's enough of them installed.

However, I'm not quire sure how the system manages this process with the hot-spare.

I have a 3U server with 6 2TB drives, 7 empty slots, then a 7th 2TB drive that's the hot spare (blinking blue light).

Question is this: If I now add TWO 3TB drives, what happens to the hot-spare (currently a 2TB)? Does the system now realize that one of the two new larger 3TB drives should become the hot-spare, convert the old hot-spare into a working disk, and therefore I'll end up with 7 "in-use" 2TB drives, a single in-use 3TB drive (acting as a 2TB), and a new 3TB hot-spare? I'd then need to add at least TWO more 3TBs to start getting more than 2TB of usable space on the new drives?

If this is the case, the old rule of thumb that you need to add THREE drives of a larger size before you gain any real advantage for the larger drives, should really be FOUR drives, since one will have to become the new hot spare. Yes?

Maybe this is an easier way to ask the question: Does the system automatically "take" one of whatever is the largest drive size installed and make that the hot-spare, removing it from storing any actual content?

Does that make sense?
 
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As I understand the system if you start adding additional drives the following will happen automatically...

The first 3TB drive will become the new hot spare releasing 2TB for storage.

The second 3TB drive will become the new K-Raid drive releasing 2TB for storage.

The third 3TB drive will give 3TB of new storage.
 
JDS is correct.


Jim
 
K-Raid Drive Utiliization

Hope the long time K users can answer a newbie question about the K-Raid drive.

From what I've read and heard, this drive contains the operating system, metadata, and user preference data files.

Seems to me that most of these K-Raid drive files would remain relatively the same size no matter how much total disk capacity (number of drives installed and the capacity of these drives), and the amount of disks imported.

Therefore isn't it a 'waste of space' if a newly added highest capacity drive is solely dedicated to storing this administrative data vs. using excess K-Raid capacity for use is storing imported disk data also.

Since this is my first post, hope I'm using the correct terminology to convey my inquiry.

Curious minds ...
 
Thanks JDS & Jim... appreciate the clarification.

Welcome Ken P - i'm sure someone will be able to shed some light on your very good question.
 
The Raid drive is actually a parity drive. RAID generally works like this:

01010100101 - Drive 1
11101010100 - Drive 2
10100010101 - Drive 3
00010101010 - Drive 4
----------------------
00001001110 - Parity drive

The parity drive looks at the data and if the bits in the strip across the drives sum to an even number, it puts a zero. If they sum to an odd, it puts a 1. Then, if any single drive is lost, the entire drive's data can be calculated out by comparing the parity bits to the rest of the array.

There isn't one drive that just holds system files. The parity drive is what allows the redundancy in the system.

The wasted space is that the largest drives become the parity and hot spare drives, but if they were not the largest (or tied for the largest) then there would be data that they couldn't give redundancy to. This may be old school, but your tape has to be longer than your program or it won't work too well. :)
 
Thanks Mr P for your response.

As a practicing non-raidiologist, guess I'd still like to know how much space is available on the K-Raid drive.

Any sanctioned method to acquire this information?

And way off target, but ... Fully realize K and it's minions are hard at work trying to ensure their survival, but is there any interest or way in renewing interest in the currently weak Scripts software capabilities?

Prior to being afforded the opportunity to own my dream K System, I had grandiose plans of being able to program the Kaleidescape system to start each or selct movie with a track from the Music Collection, then play one or more scenes, and then lower the lights, open the screen, butter and salt the popcorn, etc.

Can do many of these things except playing the music and letting K know you wish Script activation for all, random, or select movies.

Just another of my 2-cent observations / questions.
 
Ken P said:
As a practicing non-raidiologist, guess I'd still like to know how much space is available on the K-Raid drive.
Click to expand...

Like they said, the parity drive is used at the same rate as the other drives. So if all drives are the same size, you will have as much available as on any other drive (divide available space listed by n-1 (or n-2 in a 3U) to get the space on "that drive.") If they are disparate, you will have as much as any other drive, plus the difference between that drive and the next largest drive, which you cannot utilize.

Available on the hot spare: all of it, so just check the label before inserting.

Really though, the system's controller handles the load balancing, and you shouldn't be looking to yank drives... so how does it matter?
 
Thanks all for your explanation of parity drive use.

After re-reading the multiple responses, think I now sort of understand the purpose, theory, and implementation used on the 'K Drive'.
 
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