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Why use RAID5?

C

cjs06

n00b
Joined
Apr 15, 2009
Messages
12
So I have researched, built, and experienced a few RAID5 setups.

I built a NAS recently with the intention of archiving and filesharing only over a local network. It had 3 1TB Samsung HD103UJ drives in a RAID5 array running Ubuntu Server Ed. with Webmin and mdadm for software raid. The array worked fine and samba worked for filesharing. Unfortunately the raid rebuild times took many hours and write speeds dropped dramatically, which hindered the point of a gigbit lan.

My good friend became ambitious and created a RAID5 array in his desktop setup using 4 1TB drives on a Intel controller. He archived as much data as he could from external drives and finally he consolidated everything on his array. Next day one drive in the array had a few errors and it caused the array to rebuild which took over a day until a second drive caught died and dropped from the array. Now all the data is gone and he went through the arduous process of consolidating data on separate disks instead of a raid array.

What I have learned from this forum, mine and others experiences with RAID5 setups are a couple of things.

Firstly, unless you have a hardware raid controller and the money then you will have to deal with long parity rebuild times and poor performance until then.
Secondly, If one drive is dropped from the array or also while one drive is rebuilding the chances of a second drive failing is drastically higher, leaving your data at risk.

I've come to realize that RAID5 is not meant for archiving in a passive sense. Hulu, who has multiple SAN setups in many datacenters need RAID setups with parity so that they can quickly replace a dead hard drive while the array is still being used for streaming video; noting that I'm sure they have a separate SAN backing up data. This would be archiving data in an active sense because it requires that it be available 100% of the time.

I'm sharing this because I think some people don't understand the purpose of parity RAID setups, cause at first I know I didn't.

A question I do have is what other uses for parity RAID setups are there?
 
for one,. if your going to do raid 5, use a proper controller, not built in controllers

2nd, have a hot spare

3rd - RAID IS NOT A BACKUP!!!! but simply redundancy, this case is exactly why raid isnt a backup cause a 2nd drive could die while rebuilding, especially with todays massive HD's, it takes for ever to rebuild an array

4th - try raid 6 for more safety but a larger performance hit pending on raid card

5th - SATA drives can be very flakey on rebuild because it is very hard on the drives, why some companies have specic raid versions.
 
What MrGuvernment said, especially number 3.

RAID 5 is used when the data needs to be accessed without delay resulting from a single hard drive failure. In general most RAID setups are to provide uptime for heavily accessed data where a delay of any sorts could result in lost revenue, performance, business, production, work hours, etc. However it is not a form of backup or perfect storage solution.

You basically answered your own question in the last paragraph you wrote:
I've come to realize that RAID5 is not meant for archiving in a passive sense. Hulu, who has multiple SAN setups in many datacenters need RAID setups with parity so that they can quickly replace a dead hard drive while the array is still being used for streaming video; noting that I'm sure they have a separate SAN backing up data. This would be archiving data in an active sense because it requires that it be available 100% of the time
Click to expand...

That last line is the major goal of parity RAID setups: Guarantee uptime.

RAID6 is an extension of sorts of RAID 5: It is designed to protect against two hard drive failures rather than one but at a slight to major performance hit depending on the controller, size of the array, the hard drives themselves.
 
I think you pretty much answered your own question. I have very limited experience with raid 5, but from my research and what I have read here it seems that if done right ( not cheap, lol ) its a pretty decent setup. By right I mean fast controllers, raid class drives, etc. that also equates to expensive. And I also think most companies or individuals willing to invest that much will probably also go raid6. Raid 5/6 is all about uptime, not backup.
 
Yea, I'm mainly trying to create a thread that primarily defines parity RAID solutions. I have only short experiences with it and hopefully y'all can share more elaborate truths regarding. Not everyone knows.
 
cjs06 said:
Unfortunately the raid rebuild times took many hours and write speeds dropped dramatically, which hindered the point of a gigbit lan.
Click to expand...
Ummm....So? A rebuild should be a very rare occurance when a drive goes bad, not something that happens often. Which is better, slow performance or no access at all?

Secondly, If one drive is dropped from the array or also while one drive is rebuilding the chances of a second drive failing is drastically higher, leaving your data at risk.
Click to expand...
Wrong. One drive going bad does not increase the chances of another drive going bad also. Just because this was observed once does not make it fact.

A question I do have is what other uses for parity RAID setups are there?
Click to expand...
They keep business servers up and running if a drive fails, but with slower performance until the array is rebuit. Thats it. A hard drive is the most likely thing to fail in a server, so having some redundancy is a good thing.

Yea, I'm mainly trying to create a thread that primarily defines parity RAID solutions. I have only short experiences with it and hopefully y'all can share more elaborate truths regarding. Not everyone knows.
Click to expand...
There are already thousands of websites that define raid solutions as well as books if you want to read. We don't need to reinvent the wheel here. :)
 
I've been researching this topic for a while now and even purchased a Dell Perc 5/i card but I'm thinking about selling it because RAID 5 doesn't seem worth it.

I'm still trying to figure out a way to "backup" (wrong word, I know) my non-critical data such as ripped DVDs, etc. This is data I can afford to lose but would prefer not to.

RAID 5 seems too risky.
RAID 6 is too expensive (two drives out of five [in my case] is a lot to lose it seems)
NO RAID has the guaranteed loss of single drives but doesn't risk other all drives just because one or two drives die.

There is no answer it seems :(
 
jmk396 said:
I've been researching this topic for a while now and even purchased a Dell Perc 5/i card but I'm thinking about selling it because RAID 5 doesn't seem worth it.

I'm still trying to figure out a way to "backup" (wrong word, I know) my non-critical data such as ripped DVDs, etc. This is data I can afford to lose but would prefer not to.

RAID 5 seems too risky.
RAID 6 is too expensive (two drives out of five [in my case] is a lot to lose it seems)
NO RAID has the guaranteed loss of single drives but doesn't risk other all drives just because one or two drives die.

There is no answer it seems :(
Click to expand...

I like raid 10 myself.

Another option is using a raid level smarter than raid5.
Raidz in freebsd/opensolaris seems to work well.
 
jmk396 said:
RAID 5 seems too risky.
RAID 6 is too expensive (two drives out of five [in my case] is a lot to lose it seems)
NO RAID has the guaranteed loss of single drives but doesn't risk other all drives just because one or two drives die.

There is no answer it seems :(
Click to expand...

Ugh WHAT?
 
Correct me if I'm wrong but isn't RAID 10 basically RAID-1 but faster? I don't really need a lot of speed and mirroring (RAID-1) I can basically do with my Windows Home Server setup. I'd like to avoid the 1:1 loss of disk space for the non-critical stuff.

I guess I would do RAID 6 but I can't find any of them on sale for cheap and I just bought my Perc 5/i which doesn't have it :(
 
jmk396 said:
Correct me if I'm wrong but isn't RAID 10 basically RAID-1 but faster? I don't really need a lot of speed and mirroring (RAID-1) I can basically do with my Windows Home Server setup. I'd like to avoid the 1:1 loss of disk space for the non-critical stuff.

I guess I would do RAID 6 but I can't find any of them on sale for cheap and I just bought my Perc 5/i which doesn't have it :(
Click to expand...

RAID 10 is an array that is mirrored and then striped. Hence the name "RAID 10" or "1+0" which forms the number 10 when read all at once.
 
Raid1 is a better option for data safety, but uses to many redundant drives, and therefore it's to expensive, and uses to much power in my case...
 
jmk396 said:
I'm still trying to figure out a way to "backup" (wrong word, I know) my non-critical data such as ripped DVDs, etc. This is data I can afford to lose but would prefer not to.

RAID 5 seems too risky.
RAID 6 is too expensive (two drives out of five [in my case] is a lot to lose it seems)
NO RAID has the guaranteed loss of single drives but doesn't risk other all drives just because one or two drives die.

There is no answer it seems :(
Click to expand...
There is an answer. Its called an external USB disk drive and a scheduled task to copy all of your files over.
 
WHS

runs a RAID 1 like setup, but if you have a drive die and its not duplictated you only lose the data on that 1 drive not all the data on the array. its a good solution.

I run a WHS with a storage pool of 2 750gb drives and a radi 5 on a highpoint card for my 3TB of storage. I want up time, my "backup" is the phyical disk
 
Adidas4275 said:
WHS

runs a RAID 1 like setup, but if you have a drive die and its not duplictated you only lose the data on that 1 drive not all the data on the array. its a good solution.

I run a WHS with a storage pool of 2 750gb drives and a radi 5 on a highpoint card for my 3TB of storage. I want up time, my "backup" is the phyical disk
Click to expand...

I've got news for you, that's how RAID 1 always works. If you lose one drive in the array, the other drive's data is still intact. I've actualy got RAID-1 array in a degraded state for that very reason. All the data is still there and it is accessible.
 
@OP

Your friend was unlucky for sure, but what happened to him is a culmination of many factors. What model drives was he using? Which Intel controller? How good is the RAID implementation (The Linux one is pretty solid)? And so on...

The fact is that the same thing could have happened on a hardware RAID controller just as easily IF the drives are defective or have duff firmware. The on-board controller could have gone bad (has happened to me). There's loads of factors. Many enterprises use only 500GB drives, to lower the rebuild times, and therefore lower the opportunity for another drive to go bad during the rebuild.

RAID 5 is not a bad RAID level. It has its uses and its limits, just like every other RAID level. You do your research, you do your testing, and you choose the one that suits you best.
 
I haven't looked into firmware issues with my friends drives. Right now he is running them in RAID0 and he hasn't had any problems so far...*shrug*.

My original linux NAS build for some reason kept having to rebuild the array. I originally thought it was due to hard powering my box, but then I stopped that and it kept doing it. Basically the array would drop off and I would restart the box only to have it rebuild and drop performance. For a media streaming box this wasn't acceptable to me so I went with WHS and I haven't looked back.

I do however like messing with linux builds, because I can do more with them and tinker.

In retrospect RAID5 didn't suit my needs at all and only hindered them, and it is definitely expensive to do parity RAID right.
 
cjs06 said:
My original linux NAS build for some reason kept having to rebuild the array. I originally thought it was due to hard powering my box, but then I stopped that and it kept doing it. Basically the array would drop off and I would restart the box only to have it rebuild and drop performance. For a media streaming box this wasn't acceptable to me so I went with WHS and I haven't looked back.
Click to expand...

It sounds like something other than the fact that you chose Linux or RAID5 was the problem...
 
Its not a big deal anymore now, but just the fact that the setup wasn't reliable turned me off. I'm sure there is a solution somewhere, I just haven't been able to find one.

I got most of my ubuntu build info from Tim Higgins at Smallnetbuilder.com.
 
@OP

Just for clarification, are you running your WHS on the same hardware and hard drives as what you ran your Linux + RAID 5 setup on? You have my curiosity peaked...
 
I recently switched from a custom Ubuntu media server to Windows Home Server, and I have to say, I really like the setup of the OS. It is really simple and easy to use, but as a backup, I wouldn't trust it to save anything critical, even though I do have critical files on there. I have it setup to duplicate about 1 TB worth of data, and ontop of that, the entire 8 TB array gets backed-up nightly to another 8TB RAID 6-1 array i built into a safe that is only on for the duration of the backup.
 
My WHS build that I am using now is using the same hardware as before.

Mobo is an ECS Geforce 8000 series mobo with a AMD Sempron LE-1250 and a 1GB of ram.
I have 4 Samsung HD103UJ drives in there.

So far I have had no problems with the build except that WHS didn't have drivers for the GBit Lan on the mobo so I got an Intel NIC, which is overkill but it had Windows 2003 drivers and works great.

I guess originally Ubuntu probably had driver issues with the sata controller and thats why the array would drop off. This is my only guess so far.
 
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