SBS Server - RAID1 vs RAID5 for reliability

Hi Guys

I've been working with servers for a while (mostly for small business customers), when ordering new servers (Always Dell) I normally go for a mirror (2 drives) for the OS and RAID5 (with 3 drives) for the Data, the data is always backed up to tape or external USB/NAS drives as well and not totally reliant on RAID for backup purposes.

My query is, is RAID5 actually reliable?, I meet a lot of techs and some have told me they have had bad experiences with RAID5 where one drive goes down and putting in a new drive doesnt actually rebuild the data so now they only use RAID mirrors.

Secondly (and more importantly) if I did have a server with RAID1 and one of the drives failed, if for some reason the controller failed as well and I could not put in a new controller of similar type will the drive work as a standalone drive?, or put another way does the hard drive have data on it that relies on the RAID controller in any way or can I put it on another completely different bare metal system and see 100% of the data.
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Raid 5 is still reliable as ever I have used it for years and not regreded it yet.

You could see the data you would have to so a repair on the server mostly change the sid and reomce the raid controller driver.


Both questions depend a lot on the raid controller for the answer. If you use a good controller (usually not those cheap ones built into many desktop mainboards) there should note issues when you replace a failed drive whether it is raid 1 or 5. Of course you should always check the controllers manual for the exact procedure. But on cheap controllers often many weird things can happen. As for using a mirrored drive in a non-raid setup, this usually will work but some controllers write raid specific data on the disk and those disks may be difficult to get running in a non raid system.

The main issue with a failed raid 5 array is that if a disk is down, and if another fails while the new disk hasn't been rebuilt, you will loose all the data. The 2nd disk doesn't even have to fail, but a bad cable connection may cause a temporary failure, and that would cause you to loose all the data on the array. A temporary failure on a mirror on the left over disk will not cause you to loose all the data.
Lee W, MVPTechnology and Business Process AdvisorCommented:
I do not use RAID 5 anymore because of reliability AND recovery concerns.

In my experience (mostly with Dell Servers, but a few others as well), RAID 5 SCSI sets have gone off-line for no apparent reason way too often - worse still, I've seen multiple ones go offline at the same time, bringing down the array.  As for recoverability, a RAID 1 mirror, if it fails, (in MOST cases - dependent on RAID controller) will still allow data to be accessed easily, even if you need to remove it from the server and attach it to another machine.  With a RAID 5, you would need a like controller and/or special software to recover the array.

Considering the cost of drives today, the 50% overhead of a mirror is simply not very costly and provides, in my opinion, better redundancy and recoverability.

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lance_corporal_jonesAuthor Commented:
Thanks for the answers guys.

leew, just to clarify, are you saying in most cases I should be able to take a RAID1 mirror drive and put it in a completely different system and access the data? (just want to confirm theres nothing special done to the data that makes it unreadable)
Lee W, MVPTechnology and Business Process AdvisorCommented:
Yes, in most cases (every case I've personally experienced - not that I've had to do this often).  I say most because in a prior question, another expert suggested that SOME controllers, DO do something special to the drive config.
lance_corporal_jonesAuthor Commented:
Thanks leew and also rindi for your input, I think I will start going with RAID1 for future Dell servers.

I'll leave this question open a little while longer as its always good to get more input of peoples experiences, if none are received by end of this week I'll accept the multiple answers.

TristanIT ManagerCommented:
I've been working with Dell Poweredges (amongst other BRANDS) for years and I've never had a scenario where I've replaced a disk in a failed RAID5 array and it hasn't successfully rebuilt.
I think most of the horror stories come from :
1. cheap RAID controllers - I remember when the low end Poweredges had Promise IDE RAID controllers. They early ones were bad.
2. Techs who didn't read the manual and stuffed up the rebulid process.
3. Servers on unfiltered power circuits with no surge protection.

If you lose two drives then yes you are stuffed but that goes for RAID1 as well.

As for your second question I would not rely on being able to take a RAID1 member drive and slotting it into a RAID controller of another type. It might work but don't count on it.

Use a product like Acronis or Backup Exec System Recovery to create images of your OS volume and use them for easy recovery to different hardware.

For once I disagree (partially) with Leew .
I find RAID 5 to be reliable BUT it's only going to be good as the hardware and the environment that you run it on.

I agree with dextertronic as long you have a good backup program like acronis and raid 5 with good parts you can not go wrong.
I can not say again you get what you paid for when you get the budget part instead of spending a little more.

Lee W, MVPTechnology and Business Process AdvisorCommented:
Backups are ALWAYS important... but the experiences I had with various SUPPOSEDLY good RAID cards, INCLUDING Adaptec, LSI Logic, and others left me with a bad taste in my mouth.  The idea behind RAID is to increase uptime - NOT act as a backup - so backup is, to an extent, irrelevant to the question.  When you have a RAID 5 go down because a hiccup on the SCSI bus, this is BAD.  

I'll back track a *LITTLE* - RAID 5 on a nice, high-end SAN is fine.  Never had a problem with a RAID 5 on the fiber channel SAN I used to manage and I had several RAID 5s on that.  That taste (and subsequently hearing about 3WARE cards where I used to work failing on SATA and PATA RAIDs) has left me tainted to the point where I don't want to risk it on anything less than Fiber Channel.  
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