Consdering going RAID, complete noob to it

colbert · 2008-09-17 23:13:08

So my hard disk situation is I currently have 3 internal drives: 320gb, 500gb, 500gb (all Sata). I am probably going to get another 500 or 1TB soon as well. 2 are WD and 1 is Seagate.

I don't know the first thing about RAID, so hopefully the experts here and guide me as to whether or not it makes sense.

1. What are the pros and cons of going RAID?
2. I believe it treats all my drives as one drive, correct? If so, what happens if I remove on drive and if this would cause a problem, what is needed to fix it if I can't replace the drive?
3. Can an external drive in an enclosure be included in the RAID setup?
4. If I "convert" my drives to RAID, is it like a formatting of a disk or something more akin to a complete overhaul? ie., I need to backup my stuff first or can it just be done with the drives as is?

Thanks a ton for any help

Vintendo · 2008-09-17 23:26:56

Raid is there in many different forms, raid 0 combines two or more drives to make one drive as big as [the number of drives * the size of the smallest drive], it stripes the data so it can write faster. Raid one combines two or more drives to make one drive that is as big as [the smallest drive]. it mirrors the data, so if one drive fails the data isn't lost. Then there is raid 0+1 and 10 wich is a combination of one and two but requires four disks. Raid 5 combines all the drives to make one drive that is as big as [(the number of the drives * the size of the smallest drive)- the size of the smallest drive]. This secures the data, so if one fails, not all is lost and there is a speed gain.

1. Pros can be speed or security, cons can be insecurity or loss of disk space, it differs a lot per raidtype

2. In raid 1 and 5, you don't lose al your data, in raid 0 you do.

3. If it's eSata i think so, usb cannot.

4. You need to backup your stuff.

I think LVM is a nice idea for you. You can use disks of different sizes, take out disks(takes some work) and add disks. I use it and don't want to go back.

colbert · 2008-09-18 00:47:55

Thanks a lot Vintendo, that's a very helpful response.

So I take it RAID5 would be the best bet if I choose to go RAID? And I need to clean my drives first then start the process.

I just took a glance at LVM on the Arch wiki and it sounds very intriguing! A lot of the explanation is way over my head (lol) but I saw in the example that it is the same concept, I am taking all my drives and seeing them now as one yes? And so if I use LVM I would probably reinstall Arch (not a problem have everything backed up).

Does LVM provide speed gains or is it mainly convenience (the features seem quite useful for resizing and managing partitions). Thanks a lot

Vintendo · 2008-09-18 07:24:40

Remember that if you use raid 5 that with you 320gb drive and your two 500gb drive, you only will get a "big drive" of 640GB. This is the downside of raid and the reason i use lvm. LVM does not provide a speed gain, it is just convenience(but it gave me a 2.2TB partition )

afonic · 2008-09-18 09:44:58

My opinion is to stay away from RAID. The advantages of using it in a home desktop enviroment are very very minor. Plus you will waste a lot of space if you use anything but RAID 0.

Of course if you want to try, I'll let you know I run two Arch servers in software RAID0 (gaming servers) for a year now, without a single problem.

Last edited by afonic (2008-09-18 09:45:28)

fukawi2 · 2008-09-18 11:22:11

My 2.2 cents (GST inclusive)...

As mentioned, RAID on a desktop PC is generally not worth considering. The only times I would are:
1) RAID-0 (striping) for something like video editing to speed up performance.
2) RAID-1 (mirroring) for redundancy - If I REALLY don't want to loose the data, and the security of a backup on another machine isn't enough. This comes at the price of only being able to use half the purchased disk space.

RAID-5 has a fair price in write performance (because the controller not only has to split up the data in to chunks for each disk (like RAID-0), but it also has to calculate parity data). Read performance is marginally better than a single disk.

LVM on desktop's makes much more sense IMHO, although I don't use it myself (yet). You get the advantage of everything in one big 'drive', and the benefits of being able to resize all your 'partitions' to suit. You also kind of have a bit of redundancy (ie, "drive 2 has non-fatally failed, add a replacement disk, remove that disk from the LVM (LVM will move all the data from the failed disk and put it on the remaining free space) and then physically remove the failed drive). But if a drive gets totally fried, then anything on that disk is GONE (without backup).

And as a side note, if you're going to use Software RAID, you can build your RAID out of partitions, as opposed to drives, so you could technically build a RAID-10 array using only one disk with 4 partitions. But that defeats the whole purpose - you won't get performance or redundancy out of that.

Conclusion
- Unless you have complaints about the speed of your read/write performance, I'd suggest you go with LVM.
- If you want to increase your write performance, go with RAID-0 and make sure you continue to do backups.
- If you want to increase your read performance or your redundancy, go with RAID-1 with separate controllers for each disk - but remember you're going to be paying for twice as much disk space as what you'll end up being able to use.

(Just to illustrate how expensive RAID can get very quickly... I decided to put RAID-10 (mirrored then stripped) in server I built 12 months ago. We ended up with 12 drives @ AU$1,100 each, plus 2 drives in RAID-1 for the operating system - total around 200gb usable space and AU$14,000 - but this was for a mission-critical database server running operations in 4 countries.)

colbert · 2008-09-18 20:29:02

Wow, this forum is the tops, you guys are fantastic! Thanks so very much for these clear and helpful explanations! It is really making sense now.

I believe I will go with LVM and reinstall Arch this weekend with it

iBertus · 2008-09-19 04:47:19

I've got 6x750GB SATA drives running in RAID10 (linux MD driver) which amounts to about 2250GB of usable space. I use the array to store my thesis datasets and results from a hydrologic model I've been running. The Linux MD RAID10 driver can support an odd number of devices and does the stripes and mirrors in one step across all devices, so you can get the benefits with only two drives. The speed is very good, faster than a single drive, and not as slow when writing as a similar RAID5 setup. Just note that <size>*<num_devices>/2 will be the final size of the RAID10 array, while RAID5 will be <size>*<num_devices - 1>. As linux software (MDRAID) is block device agnostic, you can use any block devices listed in /dev to create the array. I would suggest 3+ drives in RAID10,f2 and partitioning using LVM. This will provide some failure proofing (two non-adjacent drives) with reads near RAID0 and writes no less than the single drive.

Arch Linux

#1 2008-09-17 23:13:08

Consdering going RAID, complete noob to it

#2 2008-09-17 23:26:56

Re: Consdering going RAID, complete noob to it

#3 2008-09-18 00:47:55

Re: Consdering going RAID, complete noob to it

#4 2008-09-18 07:24:40

Re: Consdering going RAID, complete noob to it

#5 2008-09-18 09:44:58

Re: Consdering going RAID, complete noob to it

#6 2008-09-18 11:22:11

Re: Consdering going RAID, complete noob to it

#7 2008-09-18 20:29:02

Re: Consdering going RAID, complete noob to it

#8 2008-09-19 04:47:19

Re: Consdering going RAID, complete noob to it

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