I'm just about to set up my hard drives with RAID 0. Is it really as risky as people say it is?
RAID 0 means ZERO redundancy. Whenever there is data to be written to the RAID device, it is split in two, the first part is written onto the first disk, the second part on the second, which makes your write operation pretty fast. But if either disk breaks, all your data is lost (since you lose (roughly) 50% of all your files, rendering all of them useless)
It depends on what you are using it for. As others have said it roughly doubles the risk of failure of the data on it compared to a single disk. If you had 3 disks in raid 0, then 3x the risk, etc... This because you lose almost all data if any one disk fails. RAID operates on a low level, so it doesn't generally put one file on one disk and another file on the other disk, but rather will generally split up the file between the however many disks.
However, If you have a backup, and it is static data, and uptime doesn't really matter, then it is not dangerous. For instance, I might use raid 0 on a gaming machine with my save files on another disk. This way, level loads will be fast :-) But for IT appropriate uses, its not the ideal choice.
An IT situation would be redundant machines with static data. In this case, it is okay for a machine to go down for a while.
Lastly, hard drives are mechanical, and break quite often. You might not see this if you just have a couple of desktops, but with a server room and lots of disks, you will be replacing them fairly often.
Speaking from personal experience of losing data, I'd definitely recommend you save yourself the headaches and avoid RAID 0. For each drive in the array, you increase the chances of losing all the data. I had 3 drives in RAID 0 and the middle drive broke only a few months later, losing nearly 1TB of data.
I dont think Raid 0 is risky at all. I personally run raid 0 for my os for benefited speed. You could hose my raid config any time of any day and I wouldn't lose a thing. I have my system set up correctly, to get the benefits of speed while having little to no possible loss of data.
The only risk is for people who don't know how to distribute risk.
I can say the above because I simply only work on important files on another drive than that being used to hold my OS. I install applications and stuff on my main OS drive, but their config files and such are all on a secondary drive. That secondary drive is then mirrors to another drive and I then make weekly backups of that mirror to a external drive. If my Raid 0(OS Drive) were to fail, I simply pull the drive/s out and put another one in. Take a Linux live cd and use a program like dd or cat to copy a already made image over onto the raid drives. I restart and now my system is back up to a pristine state.
RAID 0 can be a great solution in many cases where downtime is not critical.
RAID gives you speed, or redundancy or both. RAID is not a backup solution as it only guards agains hardware failure, only one type of failure that can cause data loss. So that means you need to have a backup solution in place regardless of the RAID type you use.
Regardless of the RAID type you employ you will have degraded performance in case of a disk failure or array rebuild, and since these days HDD's are getting larger and larger and speed is more or less stagnant - the rebuilt time can stretch to days or even weeks and create unnecessary stress to the disks.
I personally prefer to run RAID 0 which in case of a disk failure will be restored from backup. That to me is the faster, cheaper, less stressful solution since a bit of downtime is not really a concern.
Remember , when you are rebuilding an array , every block of data is being read / written on all disks, regardless of the quantity of useful data on the disks. In practice that usually translates on a much faster data rebuilt from backup compared to a RAID rebuild after a disk failure. Combined with significantly less write / read cycles in normal operation of RAID 0 compared with RAID 1 / 10 or RAID 5 / 6 it will translate in less disk failures overall.
All of the above is true if you have a sound automatic backup strategy in place , for example:
- continuous backup on hot files
- daily backups on cold(ish) files
- weekly backups on all files on media that is located remotely.
To minimise downtime even when using RAID 0 you can tier the hot data backup on fast mediums like and external SSD, since the hot data-set is usually small and external SSDs are quite cheap these days, and backup cold data on slow mediums. Most commercial NAS systems, event the cheap ones, will e able to do that for you these days without much of a hassle.
In mission-critical systems all of the above is irrelevant as downtime is not really an option , but even then there are still better solutions in place - like snapshots replication on ZFS, brtfs or erasure coding or server redundancy with failover systems in place.
In 99% of cases RAID-0 will probably be a bad idea for all the reasons other people have mentioned (increased chance of complete failure etc).
However it can be used in some (more extreme) situations, for instance in a large array of servers working together (a la google), where individual machine failures do not critically effect the final output, but RAID-0 is a quick and cheap way of expanding capacity.
But to be brutally honest and not trying to be mean, but if your asking such a question you won't be in the latter group of server admins :)
Lots of guys talk about probability and they are mistaken! If you want the risk of using raid 0 that is how it's calculated.
Suppose the probability of hard1 failure is p1 (in our time period unit) and hard2 is p2 then when have a series circuit because failing one hard will broke the circuit.
So to calculate the risk we have: risk = (1-p1)*(1-p2)
For example if hard1 and hard2 failure probabilities are .001 then the risk is : 0.998001
So as you see the failure of 2 hard disks almost is the same as the probability of 1 hard failure that is not too high.
But there's something else here that change the situation and that is you cannot recover files from raid broken hdds too easy, actually in my experience it's impossible.
The risk factor of using a RAID 0 depends on pretty much for what you are going to use it.
As for my experience, I started using RAID 0 a year ago using 2 inexpensive disk for improved performance in games and some video editing and 1 large hard drive for simple storage. I keep all my important data backed up where I consider to be safe.
What will I do if one (or both) disks die on me? I have an image of the SO with all my programs and drivers installed, so I'll throw the defective disk, put the other to some use until it dies like its brother, buy a couple brand new ones, and re build the array and procede to leave my computer as I want it.
Probability theory says that is P1 is the probability of device-1 failure, and P2 - for device-2, then failure of any of them occurs with a chance of P1+P2. That means, chances to lose data are really higher, actually - twice higher.
Practically, I have RAID 0, and it does not fail: HDDs have 1-2 guaranteed years of stability, and often they work ok during this period. You can monitor their S.M.A.R.T. parameters to ensure the array won't fail unpredictably.
I believe nowadays hard disks are the slowest computer part. By using RAID 0 I realized that everything works MUCH faster and the whole system is more responsive: OS loading, soft loading, .. Actually, now I'm getting tired each time I have to touch systems with no RAID inside :)
However, as Josh said, you need to make backups. Not only when using RAIDs ;)