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Author Topic: Re: RAID  (Read 12707 times)

Floydoid

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Re: RAID
« on: December 13, 2007, 01:55:37 PM »

Speaking of RAID - it's one of those terms I've heard of many times but know absolutely nothing about... so maybe it's a possible topic for yet another tutorial if anyone feels that way inclined.
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roseway

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Re: RAID
« Reply #1 on: December 13, 2007, 03:17:25 PM »

http://en.wikipedia.org/wiki/RAID

Basically it's a way of combining two or more disks so they appear as a single disk with greater performance and/or redundancy.
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  Eric

Floydoid

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Re: RAID
« Reply #2 on: December 13, 2007, 04:01:06 PM »

Hmmm sounds pretty complicated.
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mr_chris

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Re: RAID
« Reply #3 on: December 13, 2007, 08:38:37 PM »

It is, but here's a few (very basic) basics:

RAID-0 - involves using the disks to their fullest capacity. There is NO redundancy with this (i.e. if one disk dies, you lose everything!)

RAID-1 - mirroring - data is written to two hard drives simultaneously. Available capacity is only the size of one of the disks, obviously, because the other one is a real-time backup, in effect.

RAID-5 - "striping with parity" - a grand term for a pretty grand design. RAID-5 stores the data across 3 (or more) disks. The data is written to all but one of the disks in the array, and a parity check (very simple error checking) is stored on the third disk. This block of data + the parity block is called a "stripe", hence the term "striping with parity". Available capacity = total size of all but one of the disks in the array.

So say you had 4 x 100 GB disks in a RAID 5 array, you would get 300GB total storage, which is pretty efficient.

Redundancy-wise, RAID 5 allows one disk to fail whilst still preserving all the data and being fully functional. Obviously if a second disk should subsequently fail before replacing the first one, then you're pretty screwed!
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Chris

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Re: RAID
« Reply #4 on: December 13, 2007, 10:59:33 PM »

What Chris forgot to say is that RAID0 is the fastest scheme. You effectively double the speed of your disks. It is called striping.

It isn't a good idea. Ever. If you must do it then buy four disks and do RAID0+1 :)
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mr_chris

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Re: RAID
« Reply #5 on: December 14, 2007, 01:24:15 AM »

Well I deliberately didn't say it because I was trying not to encourage anyone to do it!

But yeah, RAID 0+1 is a solution, albeit a not very cost-effective one! With RAID 0+1 you get the capacity of one disk and buy 4... is any kind of (consumer) performance worth that??

*edit* deleted stupid late-night non-sensical thinking - but RAID 0+1 is still an expensive way of doing it cuz you have to get 4 hard disks! ;)
« Last Edit: December 14, 2007, 09:31:56 AM by mr_chris »
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Chris

roseway

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Re: RAID
« Reply #6 on: December 14, 2007, 07:06:08 AM »

I think I'll stick with doing backups. :)
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  Eric

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Re: RAID
« Reply #7 on: December 14, 2007, 08:17:47 AM »

Well I deliberately didn't say it because I was trying not to encourage anyone to do it!

But yeah, RAID 0+1 is a solution, albeit a not very cost-effective one! With RAID 0+1 you get the capacity of one disk and buy 4... is any kind of (consumer) performance worth that??

Heh you're not a gamer (nor am I now) but I remember when BF1942 (and mods) arrived - it took ages to load maps and RAID0 could mean you spawn 10-20 seconds quicker when a new map was loaded. Given the amount diehard gamers spend on graphics cards a few hard disks is nothing :D Loading new systems in Eve when the gate was camped benefited too...

Edit - you get the capacity of two disks Chris. Two striped and two mirrored.
« Last Edit: December 14, 2007, 08:20:19 AM by rizla »
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mr_chris

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Re: RAID
« Reply #8 on: December 14, 2007, 09:34:40 AM »

Heh you're not a gamer (nor am I now) but I remember when BF1942 (and mods) arrived - it took ages to load maps and RAID0 could mean you spawn 10-20 seconds quicker when a new map was loaded. Given the amount diehard gamers spend on graphics cards a few hard disks is nothing :D Loading new systems in Eve when the gate was camped benefited too...

Fair enough, never been hardcore enough of a gamer (I've never bothered playing online) to bother with loading times... I appreciate your point!

Edit - you get the capacity of two disks Chris. Two striped and two mirrored.

Er, that's what I meant  :-\ I blame several late nights gigging and having a smirnoff ice when I got in last night :-[
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Chris

Floydoid

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Re: RAID
« Reply #9 on: December 14, 2007, 10:34:08 AM »

Isn't this getting a bit off topic?
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guest

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Re: RAID
« Reply #10 on: December 14, 2007, 11:19:13 AM »

Yes but isn't that normal here? :)
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Floydoid

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Re: RAID
« Reply #11 on: December 14, 2007, 12:32:07 PM »

Hmmm, define 'normal'.
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roseway

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Re: RAID
« Reply #12 on: December 14, 2007, 12:35:22 PM »

You're right, it was getting off topic, so let's just draw a line under it.
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  Eric

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Re: RAID
« Reply #13 on: December 14, 2007, 12:47:00 PM »

Topic split and moved so that discussion can continue without distracting from the linux stuff :)
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Floydoid

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Re: Re: RAID
« Reply #14 on: December 14, 2007, 03:35:01 PM »

I'm beginning to understand the principals now - but still can't visualise what a typical RAID setup would actually look like.
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