Author Topic: I thought I understood raid until now!  (Read 1416 times)

Offline juise

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I thought I understood raid until now!
« on: October 19, 2011, 06:14:27 am »
Let me start by saying FlexRAID is awesome! It takes raid far beyond the basics, and sadly thats probably why I'm so lost :) You can do SO MUCH with it that you could never do with standard raid I'm having a hard time figuring out some aspects of it, and how they relate to what I would like to do. Please excuse me if I'm missing something obvious, thats why I'm asking. I have read through a lot of the FAQ and setup guides, but I still have questions.

I have is a Win 7 box with
1x150Gb (OS Drive yes I know it can't be part of the raid)

7x500Gb
1x1Tb (with 700Gb of data)

I think I can safely use Snapshot RAID for what I want. This is basically my media share for music, pictures, and video. But I want to feel safe archiving family photos to this RAID.

The easiest way for me to understand it, is to look at a UoR as a 1 to 1 for a measure of data. So if I always want to be able to recover at least one drive, my PPU has to be equal to the size of the largest drive in the RAID (either the 1TB disk or 2x500GB)? If this is correct, does that stay true no matter how big the RAID gets as long as the drives are 1TB or smaller? If so thats really impressive!

Whats the advantage of Snapshots over realtime? I suspect Realtime has a larger performance overhead compared to snapshot when its not syncing. But realtime is not vulnerable to data loss as a result of a failure in-between syncs. Anything else I'm missing?

Can I change PPU later? Say I want to add a 2TB drive. Can I set the new 2TB as the PPU, and move the old PPU to the DRU?

When syncing a snapshot does FlexRAID know what it has to change in the RAID, and just do that, or does it have to check every file in the RAID regardless of whats happened with the data? So if I make 10GB of changes to the raid thats has 1TB free of 3.5TB, am I waiting for it to sync the 10GB of data, or the entire 2.5GB of data in the RAID?

Is a pool is pretty much JBOD?

I guess I'll stop here. There is so much FlexRAID can seem to do I just want to make sure when I do it, I do it right.

Offline xliv

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Re: I thought I understood raid until now!
« Reply #1 on: October 19, 2011, 07:08:31 am »
Hi,

The easiest way for me to understand it, is to look at a UoR as a 1 to 1 for a measure of data. So if I always want to be able to recover at least one drive, my PPU has to be equal to the size of the largest drive in the RAID (either the 1TB disk or 2x500GB)? If this is correct, does that stay true no matter how big the RAID gets as long as the drives are 1TB or smaller? If so thats really impressive!
Yes this is true

Quote
Whats the advantage of Snapshots over realtime? I suspect Realtime has a larger performance overhead compared to snapshot when its not syncing. But realtime is not vulnerable to data loss as a result of a failure in-between syncs. Anything else I'm missing?
Well, stability is one of the biggest difference: Snapshot is ready to be used, RealTime is alpha.

Quote
Can I change PPU later? Say I want to add a 2TB drive. Can I set the new 2TB as the PPU, and move the old PPU to the DRU?
Yes, you can change the PPU later, there are articles about it in the wiki about migrating your parity data to a largest drive: look here for ex: http://wiki.flexraid.com/2011/07/05/process-for-expanding-snapshot-raid-dru-ppu-size/

Quote
When syncing a snapshot does FlexRAID know what it has to change in the RAID, and just do that, or does it have to check every file in the RAID regardless of whats happened with the data? So if I make 10GB of changes to the raid thats has 1TB free of 3.5TB, am I waiting for it to sync the 10GB of data, or the entire 2.5GB of data in the RAID?
It is doing change management. As an example, with my setup (16TB of data), RAID creation will take around 12 hours, and update/sync will take as low as 30mn depending on the change that was done since last update[/quote]


Quote
Is a pool is pretty much JBOD?
It is better than JBOD:
- drives can still be read independently
- if you lose 1 drive, the rest of the content can still be accessed
- you can distribute data as the JBOD (fill each drive one by one), or in a balanced way
- you can remove a drive from the pool at any moment

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