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VhyVenom

Read Striping limits? Why does it fall back to one disk

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Hi,

 

What are the limits of read striping? For example if I transfer from a folder the is 3x duplicated I expect it would pull from all 3 disks of that file, correct?

 

How come it starts off with 3 disks then falls to 1 after a period of time? I would expect it to use all 3 disks for read striping (for the whole copy)? All the pools disks are on the same controller. For testing I am copying from the Pool volume to OS SSD (which is on a different controller).

 

When I transfer from DrivePool volume over network it engages 3 disks, then falls back to one after about 15 seconds.

 

Also what is the light blue color and dark blue bar indicate? How should i interpret Percentage of Read striping?

 

Will go do some searches.

 

~v

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http://stablebit.com/Support/DrivePool/2.X/Manual?Section=Performance%20Options

 

 

Basically, if one or more disks are much slower, it will only read from the faster disk. 

 

As for copying from the same controller, that really depends. In fact, depending on the controller, reading from three disks on the same controller could be slower overall than reading from just one disk. It may be spreading out the IO and adding additional overhead to do so. That may not be happening, but it is a possibility.

 

As for the different colors for the performance UI:

http://stablebit.com/Support/DrivePool/2.X/Manual?Section=Performance%20UI

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Ahh the MANUAL. For a kid who said never gonna read a manual... its time to read the manual. Just FYI maybe make it really standout on the website? I had no idea the manual existed, was actually searching through old blog posts (which are extremely helpful) and forum threads to glean data about the features - but a manual is a great way for me to familarize myself with the underlying concepts and execution.

 

I see read striping is a more complicated matter than initially meets the eyes. I did a test where i basically grabbed random files, some ginourmous, some small some medium and intiated a transfer to a local SSD. That is when I understood just why in the world you would want several different algorithmic approaches to handle different requests during read striping especially when dealing with platter drives. I am pleased to report DrivePool successfully maintained just about a full pipe throughout the transfer thanks to its alogrithmic approach in its read striping implementation.

 

For just one person reading a single file from the DrivePool it seemed odd on WHY wouldnt DrivePool just blindly do a even split between the duplicated data. Throw in some more users or generate a workflow that is handling different kinds of data (say batches of pictures which are small + bunch of home video which is medium + ripped Blu Rays which are LARGE) and you see that approach is rather clevely thought through for multiple use cases,

 

All in all I am pleased from what I am seeing with Read Striping - at the end of the day my transfer pipe is regularly FILLED to capacity thanks to read striping. And I think that is probably the main metric that matters here.

 

now the only thing I need is a bigger pipe (10gbE?) to fill.

 

thank you,

v

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Yeah, the manual needs work. We'll see about cleaning that up.

 

As for read striping, yup, definitely complicated. Very. But glad to hear that it performs very well for you. Performance is one of the things that we try to optimize for (after stability, of course).

 

And yes, bigger pipes would be nice!

If this is over the network, look into 10gb NICs. They make them, and they may work great. Not cheap though. Also, there is bridging, teaming, link aggregation (spelling?). These may help boost the max throughput for you.

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