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#1 2006-08-31 16:18:11

Mr Green
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From: U.K.
Registered: 2003-12-21
Posts: 5,893
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Is raid the way to go?

Hi,

I'm thinking now about setting up raid1 on my system

Wiki guide does not make any sense to me, do I have to reinstall Arch?

do you need to make /boot /swap raid ?

I thought (maybe wrongly!) that raid1 mirrored drives?

:?


Mr Green

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#2 2006-08-31 18:32:07

nogoma
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From: Cranston, RI
Registered: 2006-03-01
Posts: 217

Re: Is raid the way to go?

I'm running raid 5 on my system, relatively pain free. I use it so as not to loose all my precious data wink. If you have the extra HDDs, I'd say give it a shot.This site has a relatively brief overview of the different RAID levels. Don't put /boot on RAID, as your system needs to be able to read the boot info (i.e. it won't be able to load the boot partition if it can't assemble the raid device, but it can't assemble the raid device until the boot partition is read...). Since I'm running raid-5 (not a performance RAID), I only put my critical data in the RAID partition, and stuff like the system binaries and such I keep on a normal partition, for efficiency. Perhaps somebody that's running RAID-1 can recommend what partitions are good candidates for going onto the raid device. Depending on what hardware and stuff you have lying around, you don't necessarily have to reinstall Arch, you may be able to migrate over (i.e. if you have new HDDs on which you want to set up the RAID, and can keep your old system on your current HDD, and just migrate stuff over, then remove the old drive when done). It's probably easier to do a reinstall though, as there's less worrying about making sure everything migrated securely.

Having said all that, setting up RAID isn't necessarily trivial. I followed the this wikipage, but I see that there is a Converting a single drive system to RAID page as well, which is probably more up your alley. It's pretty easy to end up with a pretty messed up system if you're not sure what you're doing, so make sure you do enough reading/ask enough questions to be pretty certain of what you're doing before you dive in wink.


-nogoma
---
Code Happy, Code Ruby!
http://www.last.fm/user/nogoma/

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#3 2006-08-31 18:39:04

mouse256
Member
From: Antwerpen, Belgium
Registered: 2005-08-24
Posts: 247

Re: Is raid the way to go?

I'm using software raid here too...
Note that there is a difference between hardware raid, bios raid and software raid.
Hardware raid: you need an expensive card for it
Bios raid: what most (windows) people use and most recent motherboards have. You can boot from it, but you need a driver for it, and mostly these drivers aren't that good
software raid: you cannot boot from it (but an small non-raid boot partition with an initrd/initcpio can do the trick). it's a lot more flexible, you can make parts of it raid1, parts of it non-raid, parts raid0, ...

Installing arch on raid0 can be tricky (I couldn't get the installer detect/create my raid array, so I had to install arch on another copy and then cp -a it to the raid partition using a gentoo live cd)
I have my / on raid0 (speed), /home on raid1 (safe) and some parts non-raid (windows)

my swap is also non raid, I read somewhere it was better to have 2 swapfiles on every disk, and that the kernel itself would use the swap in such an optimal way, even better than the swapfile was on 1 raid0 disk.

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#4 2006-08-31 19:42:05

Mr Green
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From: U.K.
Registered: 2003-12-21
Posts: 5,893
Website

Re: Is raid the way to go?

Wow so much to take in

I read an article in linux format about setting up raid1 that what got me interested

got 2x250gb sata drives Arch is on one the other is empty I thought that I could just mirror my /root & /home (raid1)

If read it right it would mean that my sda would be backed up on sdb & should one drive go down the other still functions

/boot does not need to be raid do not see any point in making it so....

Do not mind the idea of reinstalling Arch just do not see thats its required (unless you know different!)

One other problem (not a major one!) is I have no swap partition :shock: lost it when moving drive to new machine... would a swapfile be ok .. or should I create a partition say twice my ram 2G?


Mr Green

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#5 2006-09-01 07:19:05

mouse256
Member
From: Antwerpen, Belgium
Registered: 2005-08-24
Posts: 247

Re: Is raid the way to go?

Raid 1 is indeed a mirror, when 1 goes down, you loose nothing.  With raid 0 you loose everything when one of both goes down.
So:
raid1:
+safe
+reading speed is high (has the same data on both drives, so can combine the read)
-you loose half of your diskspace
-writing is normal speed
raid0:
+reading and writing is fast
+you don't loose any speed
-(very)unsafe

that's why I have my / on raid0 (I don't bother to loose my arch installation on a crash, you can just reinstall) and my /home on raid1

It seems logical to me that for creating a raid1 you don't need to erase everything, but I can't confirm that.
about the swap issue: I have no idea wink

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#6 2006-09-01 07:31:03

Mr Green
Forum Fellow
From: U.K.
Registered: 2003-12-21
Posts: 5,893
Website

Re: Is raid the way to go?

Woah! thanks...

Swap I could use /var partition (move var out to root part.)

or just re-size partitions ... could do with a media one ;-)

Best thing to do is backup ... & give it a go..

Have a spare 80gb drive laying around for backup/extra storage may drop that in

No I would lose in affect 250gb ... but that does not bother me drives are getting so cheap these days ......

What I paid for my 80gb would buy a 250gb now  :shock:


Mr Green

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