Raid

Dear,

I am specifying server to be used for solid waste management system, I am wondering if RAID 5 would be ok.... or there is another option that you may want to advice.

thank you!

Charbel

What is the intended use of the server?

What do you want Raid to do for you?

to provide redundancy to the system... any drawbacks from RAID 5?

thanks!

charbel

Define redundancy?

Raid protects you against hard disk failures, that is it. I would not classify it as redundancy.

How much do you want to spend?

Raid 1 will work - $$
Raid 5 will work - $$$
Raid 10 will work - $$$$
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.
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Not really any draw backs other then you lose a full HD of space in the array.

It's pretty convienent to hot swap the dead drive and just have the raid array rebuild itself. As long as someone notices before the next drive dies.

thank you for your replies.
I will be having one historian server and dual redundant data servers.
and the application will be for solid waste management system.
in what raid 1 will differ from raid 5 from raid 10 if redundancy is needed to recover from one disk failure.

Let's clear up a few things. In today's world you should only be using RAID 1,6,10 nothing else makes sense. RAID 5 has not been useful since about 2007.

Stay away from RAID 5 at all costs.

There are too many rebuild issues with today's drive sizes and configs on RAID 5 when 1,6,10 are just as affordable.

It depends on the type,frequecy and amount of data you will have also. You can't make a good RAID decision based on the info you have given.

Also don't waste your time with fake RAID. Make sure you have a real raid card if you need reliability on your server. If you plan on have over 2TB of data I would not consider anything less than RAID 10 due to the parity and rebuild times.Any raid that is built in on the mother board is fake raid no matter what they say.

Don't make the mistake of taking RAID as a backup as it's not backup so make sure you have a reliable backup method in place in addition to raid.

If you need server reliability you should consider some other technologies as disk failure is low on the list in the causes of server failures / issues these days.

dear,

thank you for your replies,
however, I have a question, referring to below

http://www.dell.com/learn/us/en/04/campaigns/dell-raid-controllers

Most of the PERC products supports different level of RAID so I cannot really get the difference in price between Raid 0, 1, 5, 6, etc..

say we choose PERC H310 it supports many raid levels such as 0, 1, 5, 10 and 50 so where the difference in price between different RAID levels?

thanks!

Charbel

Whilst I don't doubt that PLC Kid is right about new systems we have a number of Poweredge servers running RAID 5 without any problems with rebuilds. The bigger issue we have is with the reliability of the Dell RAID controllers (PERC 5i) which are easily the most problematic part of the systems. We changed to HP hardware a couple of years ago and have had no problems at all with their servers.

A while back I came across this site that helps visualize raid types.

http://www.acnc.com/raid

Andybr said:

Whilst I don't doubt that PLC Kid is right about new systems we have a number of Poweredge servers running RAID 5 without any problems with rebuilds. The bigger issue we have is with the reliability of the Dell RAID controllers (PERC 5i) which are easily the most problematic part of the systems. We changed to HP hardware a couple of years ago and have had no problems at all with their servers.

Click to expand...

If you are running RAID 5 on todays larger disk sizes on an array of any useful size you are playing with fire for your rebuilds no matter what controller your using. The issue is not the controller but the disks. Using SATA disks are adding gasoline to that fire.

RAID arrays are groups of disks with special logic in the controller that stores the data with extra bits so the loss of 1 or 2 disks won't destroy the information (I'm speaking of RAID levels 5 and 6, not 0, 1 or 10). The extra bits - parity - enable the lost data to be reconstructed by reading all the data off the remaining disks and writing to a replacement disk.

The problem with RAID 5 is that disk drives have read errors. SATA drives are commonly specified with an unrecoverable read error rate (URE) of 10^14. Which means that once every 200,000,000 sectors, the disk will not be able to read a sector.

2 hundred million sectors is about 12 terabytes. When a drive fails in a 7 drive, 2 TB SATA disk RAID 5, you’ll have 6 remaining 2 TB drives. As the RAID controller is reconstructing the data it is very likely it will see an URE. At that point the RAID reconstruction stops.
Here's the math: (1 - 1 /(2.4 x 10^10)) ^ (2.3 x 10^10) = 0.3835
You have a 62% chance of data loss due to an uncorrectable read error on a 7 drive RAID with one failed disk, assuming a 10^14 read error rate and ~23 billion sectors in 12 TB.

Today you don't use RAID 5 on any data that you care about. RAID 5 in any decent sized arrary is almost like have no protection at all and a very big gamble. I have seen it fail more times than I can count.

When you can use RAID 10 for almost the same cost choosing RAID 5 now is a foolish choice indeed.

Charbel said:

dear,

...
say we choose PERC H310 it supports many raid levels such as 0, 1, 5, 10 and 50 so where the difference in price between different RAID levels?

.....

Click to expand...

Price difference is in the number of hard drives in use for each RAID type.

Raid 1 you need 2 disks
Raid 5 you need minimum 3 disks
Raid 6 you need minimum 4 disks
Raid 50 you need minimum 6 disks
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etc.

Notice "minimum", depending on the disk size you choose and the amount of total disk space you require, well you may need more disks than the minimum.

So, the price is all about the type of disk you choose, the size of disk you choose, the amount of total disk space you wish to have and finally, the requirements of the RAID type you wish to go with.

RAID cards will support many different types of RAID, but it's limited by other hardware factors in the system.

I think you need to read up on RAID.

Kid what do you consider to be a "larger disk size"? 1TB? 2TB? I don't spec server hardware all that often so I'd like some education if you don't mine. Generally I have seen others spec RAID 5 setups using 300GB 10K SAS disks, this includes corporate IT types. They usually shoot for 1.2 TB of total disk space (obviously this is all about the application). Seems like this is reasonable for RAID 5?

Just curious where you draw the line.

Paully's5.0 said:

Kid what do you consider to be a "larger disk size"? 1TB? 2TB? I don't spec server hardware all that often so I'd like some education if you don't mine. Generally I have seen others spec RAID 5 setups using 300GB 10K SAS disks, this includes corporate IT types. They usually shoot for 1.2 TB of total disk space (obviously this is all about the application). Seems like this is reasonable for RAID 5?

Just curious where you draw the line.

Click to expand...

If someone had a gun in my mouth and I had to do RAID 5 I would not use any larger than 300 GB disks and would not do an array any larger than 1.2 TB.

Consider this a 6 disk 12TB RAID 5 array 6x2 TB disks has a 50% chance of failure upon rebuild and those are not good numbers for data you care about or uptime you care about.

In your example on RAID 5 you are 80% storage efficient and have a fault tolerance of 1 drive and a theoretical read performance of 4X and a theoretical write performace of <1x which is poor.

Use the same disks in a RAID 10 config but use 8 disks Vs 5 and you have a fault tolerance of 4 vs 1. None of the rebuild reliability issues and a theoretical read performace of 8X and a theoretical write performance of 4X.

Paully's5.0 said:

Kid what do you consider to be a "larger disk size"? 1TB? 2TB? I don't spec server hardware all that often so I'd like some education if you don't mine. Generally I have seen others spec RAID 5 setups using 300GB 10K SAS disks, this includes corporate IT types. They usually shoot for 1.2 TB of total disk space (obviously this is all about the application). Seems like this is reasonable for RAID 5?

Just curious where you draw the line.

Click to expand...

If you see anyone in IT that uses RAID 5 now then the employer may want to consider getting some new IT employees because they have a very outdated understand of storage technology and if they are using RAID 5 they are setting up very unreliable systems as far as storage is concerned.