RAID 1, explained

Quick explanation of how RAID 1 works.

Category:

Science & Technology

Tags:

• RAID
• Technology
• Hard
• Disk
• Drives
• Windows
• Apple
• Microsoft
• OSX
• Leopard
• Redundancy
• Array

[Bentace]

what if one of my HDD's fails in RAID 1 and i insert a new HDD with lower capacity than the new dead HDD.. Will it warn me that the first living HDD with my data cannot copy to the new HDD because it's full?

[sn0le]

@Bentace:

I don't know. I've never tried that.

The only thing I've tried is putting a larger disk back in the array.

And then the RAID controller would only use half of the largest drive, since that drive was twice the size of the original drive.

[Paratrooper1n0]

@sn0le

What happens if you use 3 or 4 HDD's does it increase reliability (are the same file sent to each HDD) or what?

[sn0le]

@Paratrooper1n0:

If you have a RAID-controller that supports more than 2 HDDs in RAID 1 it will increase realibility.

(But I'm not sure that this is common).

With 2 HDDs you'll be safe from harddrive failiure in 1 HDD. If 2 HDDs fails, you'll be screwed.

With 3 HDDs you'll be safe from harddrive failiure in 2 HDDs.

With 4 HDDs you'll be safe from harddrive failiure in 3 HDDs. Etc.

You always have the choice to go with RAID0+1 or RAID1+0 with 4 drives.

Just a question of redundancy vs capacity.

[sn0le]

@Paratrooper1n0:

If you have 3 or 4 drives in RAID 1, the drives will contain exactly the same.

They will all be mirrors of eachother.

So this is probably used only if the data is VERY important.

I use 2 HDDs in RAID1 on my fileserver.

I also have an external backup HDD so that I have a complete backup of the array in case of total failiure.

I feel that this solution is sufficient protection of my important files.

[KINGof100KINGs]

how does this works!! is raid controller is on the motherboard OR on PCI-E??

[sn0le]

@KINGof100KINGs:

It can be both. Many motherboards have a Disk-controller that has RAID functionality.

Usually it requires some kind of software within the OS to work, like Intel Matrix Storage.

Or you can use a dedicated PCI or PCI-express RAID-controller.

Another option is software RAID, where the OS itself works as a RAID-controller.

For professional solutions a dedicated RAID-controller card is mostly used.

[parahumanoid]

@yapanuwan

Ok, even 2-drive raid 0 doesn't give you an exact double rate in reading. On raid 1 there is "some" increase, because both disks can read the data independently saving you on seek times. You actual performance gain will depend on whether your data is heavily fragmented, amount of data in question. The exact way your raid controller is programmed also matters for whether your read rates will be close to double.

[sn0le]

@yapanuwan:

True. I decided to edit that part out.

The reason is that the performance boost will not always be the same.

Usually the read performance will be double of what a single HDD has.

Write speed will usually be the same as a single drive.

In some cases it might actually be lower.

[yapanuwan]

What about increased Read Speed ? You didn't explain that !