Do you use RAID - if so, what type?

[eean]

Got an opportunity to redo our hard drives so I thought I might go for RAID. Only software, I'm afraid, but apparently that's still better than no-RAID. So, do you have RAID 0 (mirror),1 (striped) or 5 (striped with parity)?

Having done some research on the webnet, some places say you'd be a complete fool to use RAID 1 for anything other than swap files etc... But, with a good backup strategy it should be fine?? We're talking about staff and pupil data here and running some software, plus software distribution.

Other places say the CPU load, and delay in writing (especially small files) is really high with RAID 5. Is none of this offset by the fact you are sharing the write between 3 drives?

 

Or will I not even notice the difference and not bother with RAID at all? Do other factors (such as network interface) become the weaker link? 1 Server doing all jobs (print, wsus, file, domain etc..) 700mb, 1.5ghz. 50 computers. Primary school. Some software run from the server. Currently 100mbs network card but might upgrade this to gigabit if I get round to it. (Have gigabit port on the switch).

 

Thanks!

[webman]

Hardware RAID5+ on one MIS server and software RAID1 on our web server.

 

Software is always slower than hardware, especially with RAID5 as it has to write to all disks in the array every time.

[Busybub]

We use RAID5 and RAID1 on different servers. Try to use 5 if the hardware allows, but some of our stuff only does RAID1.

 

Tried software once but the speed difference is noticably slower. Wouldn't bother again considering you can get a decent PCI based RAID5/1 card for 45 quid, or a cheap RAID1 only for less than a tenner.

[timbo343]

We use Raid 5 on the 2 file servers with a few drives mirrored (Raid 1) and then on some other servers (raid 0). It depends on the importance of the server and what it does. To be honest, Raid can be a bitch when it dies or the server goes down

[Norphy]

All of our servers have mirrored boot drives, some with hardware RAID controllers, other with software. The file servers, SQL servers and email servers have RAID 5 for their data volumes. We did have a RAID controller which did RAID 3 at one point but it was pants.

[maniac]

All our servers also have RAID 1 (mirrored) boot volumes, and if they have local data storage, this runs RAID5 or RAID1 as well depending on the number of drives.

 

Our storage server (which has an array of 9 250GB SATA drives) runs RAID 6+1 which is an extension to RAID 5 and also gives us a spare 'hot' drive incase one fails. This spare drive jumps straight in and the array is re built straight away in the event of a drive failure. In theory 2 drives could fail at once on our storage array and we'd be ok.

 

Reason we went for this is this storage array stores ALL our data for the entire network, (excluding exchange and SQL which are both stored on their local servers.) so it's critial it doesn't fail, and given this schools history of data going missing, we wern't taking any chances!

 

I can't even imagine managing a server now that doesn't use RAID, as the thing with hard drives is it's not if it fails, it's when! On average we have to replace one drive every 3 or 4 months (we do have a lot of drives in our servers thou) Imagine if we didn't have RAID, all that downtime and resotring from backups, makes me shudder to think about it!

 

Mike.

[CyberNerd]

Tried software once but the speed difference is noticably slower. Wouldn't bother again considering you can get a decent PCI based RAID5/1 card for 45 quid, or a cheap RAID1 only for less than a tenner.

 

These cheap RAID cards are technically software RAID, they are also known as fake raid. True hardware RAID is where the OS driver is unaware of the underlying disk and the OS driver only sees RAID arrays. In fake RAID the OS and the BIOS in the card provide software RAID. Linux software RAID is actually faster than fake RAID and as a result nobody bothers writing Linux drivers for these cards.

[sidewinder]

5 out our 6 main servers have hardware RAID 5

The other main one is the ISA server so didnt really need it, thats software mirrored

[ajbritton]

RAID 5 is a bit pointless now that hard drives are so inexpensive. I believe RAID 10 (or 0+1) is the way to go. This is a combination of mirroring (to give resiliency) and striping (for performance).

 

RAID 5 suffers from what is known as the RAID 5 write penalty. Every time data is written to the array, all the disks must read some data so that the parity can be calculated. It's therefore essential to have write caching on servers which have high data write rates. This is a risk as if anything dies, the write cache will evaporate and corrupt the array. This means a battery backed cache is essential.

 

EDIT: Also, avoid software RAID at all costs!

[bossman]

ajbritton:

 

I have to disagree with you on this one as i have had good experience of hardware raid 5 which really saved my bacon when one of the drives went caput i didn't even notice it as the raid was reconfigured from the parity information from the other drives automatically which rebuilt the redundant drive and never missed a beat. This was on our MIS server too.

 

Have a quick read of the tutorials below i feel you may have been mis-informed

 

http://www.acnc.com/04_00.html

 

P.S agree with you totally on software raid.

[CyberNerd]

Actually the software RAID = bad argument isn't always the case, there are many situations where software raid is preferred. Software raid is more flexible, (does your hardware raid controller email you if a disk fails?). It is certainly cheaper compared to 'real' RAID cards and software RAID can actually be faster than hardware RAID (as it's dependant upon processor speed rather than hardware controller), there is a detailed list of pros vs cons here. Of course this applies to linux raid, windows software raid does suck.

[DMcCoy]

I use Raid 1+0, 1, 0+1 and 5. I also don't like software RAID, and even took a 50% space cut over using it on the Mac servers with the xraid!

[ajbritton]

@bossman: I'm not saying RAID 5 does not work, but I stand by what I said. RAID 10 or (0+1) will give better performance than RAID 5. The site for which you posted a link says that RAID 10 and 0+1 given better I/O rates than RAID5.

 

RAID 5 only gives moderate write performance. If a disk fails, performance will be rubbish (until drive is replaced or hot swap spare comes fully online) as the controller needs to reconstruct the missing data from the parity information striped across the remaining drives.

 

RAID 10/0+1 gives excellent write performance (because the data is striped) and does not degrade if a disk fails (because the data is mirrored).

 

I would concede that ultimate write performance is probably not an issue for school file servers (although if you are trying to get the best out of SIMS, every little bit probably helps), but I think the reliability aspect does it for me.

[eean]

Well... It doesn't matter now! I put my spare hard drive in an it went 'Click... Click... Click'. Hmm... not a good start - RAID or no RAID. This drive was sent to me last year, 4 days after I needed it as part of the RM Next Day Onsite service agreement. Well that was a couple of hundred quid well spent!

[localzuk]

I'm likely in the same boat as everyone else. Generally, our servers have RAID 1 for the boot volume and RAID 5 for the actual storage, but this varies (depending on how many disks are in the server...).

[contink]

Went with RAID 5 for 3 sites now... The latest has 3 drives + a spare..

 

One lesson learned was not to use motherboard based raid and use a replaceable RocketRaid PCI-E card. I had in the past used a motherboard RAID array and lost everything (well until the backups came in) because the motherboard was no longer available and thus neither was the data.