RAID 1 vs. RAID 5

bangshi

bangshi

bangshi

Associate
Joined
29 Jan 2013
Posts
5
I require 8TB of usable space.

I am trying to find the ideal RAID set up to maximise performance against cost.

Is the performance hit of RAID 5 detrimental to the point that it is worth the additional cost of additional drives for a mirroring RAID 1 setup?

Also, a question about RAID 5 - can I set one up with the minimum of 3 drives and just add additional drives as required to the array with ease? Is there any kind of time to wait for it to build to take into account the new drive in the array?
 
Will you be using a raid card or anything? Raid 5 I believe can be fairly slow if just using the mobo itself.

As for expanding the raid array, I'm not sure unfortunately but I would imagine you'd need to recreate the array - but I could be wrong on that.
 
Maximising performance against cost will lead you to raid 0. Minimum number of hard drives, maximum performance. Significantly less reliable than JBOD (just a bunch of disks). Raid is about minimising downtime. That's all. It's not a backup. It's not particularly cheap. If you want to go ahead regardless...

Raid 5 uses fewer drives than raid 1. It is also less robust. In particular, one disk fails, and you replace it. The array then rebuilds, placing unusually high stress on the remaining drives. If a second falls over before the array rebuilds, it's restore-from-backups time. I'm now using two 2-disk raid1 arrays instead of one 4-disk raid5 on the basis that it's more likely to survive drive failures.

Raid 5 performs well. Write speeds comparable to writing to a single drive, read speeds significantly higher. That's my experience with software raid under linux. Similarly building an array with three drives and adding another (to increase storage space, not as a hot spare) works fine (mdadm under linux). Some systems will struggle with this - zfs' raid version won't let you add drives. I don't know if motherboard raid will allow you to add drives - I don't like the idea of the array being tied to a single board in case the board goes bang so haven't tried it.

Raid is not usually a good idea at home. It essentially doesn't matter if a drive dies, leading to a couple of days downtime while you buy a replacement / RMA it then restore from backup. It is a valid means of increasing performance but all too often seen as a replacement for backups.
 
Last edited:
Thanks for the replies. When I say performance I'm not really looking for gains, just not looking for big performance losses compared to single drive.

When you say RAID is not ideal for the home and better off with backups, what do you suggest? The only alternative I can think of is optical disk backups but that is time consuming for terabytes of data!
 
RAID isn't really a backup solution. It assists in downtime recovery, normally for servers, so if a drive fails then the redundancy is spread across the remaining disks so the system is still usable but in a restricted state until the faulty disk is replaced. Bear in mind though, that RAID 5 is not a mirror. it uses parity over the disk which is what you only need a minimum of 3 disk.

An ideal home backup solution is to have a secondary hard drive, and use backup software to either sync or mirror.

My set up for example:
Drive 1 SSD for OS and Apps
Drive 2 (HDD) for all files. I've moved the user files from the default C: partition to this drive.
Drive 3 (HDD) back of of Drive 2

I use SyncBackSE to back up daily, but you can use Synctoy, FBackup etc.. All do the same thing.
 
OK, so in that scenario I could have two or three drives set up as a spanned disk in Windows and then an additional two or three drives as another spanned disk and sync between them. This sounds a bit more simple.
 
8TB of usable space you want? RAID1 is a mirrored pair of Hard disks. You would need to have multiple arrays to achieve 8TB. i.e. Currently the largest Hard disks are 4TB each.

Assuming you use 2TB disks which are still currently the best price per GB (most of the time, unless you see a very good 3TB deal):

RAID5 = 10TB required
2TB disks @ £70 each = £70 x 5 = £350

The thing to be aware of with Raid5 is that if the Motherboard or Controller card dies (assuming hardware based) then your data is all gone. You can't take your disks and fire them up in another machine and get your data back. You would need to buy an identical mobo/card to try to bring the array back online and provide readable data.

If a RAID1 array dies, the data on the non failed side of the mirror is still available if you were to mount the disks elsewhere to read them.

Do you want to run this RAID array in your current PC or as a separate server? What requirements do you have in terms of speed?

RAID is not a backup.
 
jaybee said:
8TB of usable space you want? RAID1 is a mirrored pair of Hard disks. You would need to have multiple arrays to achieve 8TB. i.e. Currently the largest Hard disks are 4TB each.

Assuming you use 2TB disks which are still currently the best price per GB (most of the time, unless you see a very good 3TB deal):

RAID5 = 10TB required
2TB disks @ £70 each = £70 x 5 = £350

The thing to be aware of with Raid5 is that if the Motherboard or Controller card dies (assuming hardware based) then your data is all gone. You can't take your disks and fire them up in another machine and get your data back. You would need to buy an identical mobo/card to try to bring the array back online and provide readable data.

If a RAID1 array dies, the data on the non failed side of the mirror is still available if you were to mount the disks elsewhere to read them.

Do you want to run this RAID array in your current PC or as a separate server? What requirements do you have in terms of speed?

RAID is not a backup.
Click to expand...

I would suggest a RAID 10 array which splits your data over several drives like RAID 0 but also makes sure that each drive has a mirror, so if any one fails the whole array can still function.

Alternatively, you could have a RAID 4 software solution, where there is one parity drive as big as your largest data drive which can recover an infinite number of data drives. The main advantage of a software solution such as this is that they keep your drives readable by other computers, as all the parity data is just stored as parity files on the parity drive. This also means that if you have multiple drive failures, you only lose the data on those drives, whereas in hardware RAID 5 the parity is spread across all the disks, so if more than one drive fails you lose the whole array.

Examples of software solutions are Disparity and SnapRAID (free), or FlexRAID (paid).
 
You must log in or register to reply here.
Back
Top Bottom