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I am planning on setting up a RAID 5 array on my data storage drives using Windows Server 2008 software RAID. I currently have a 500 GB drive for the server OS and two 1 TB drives for data storage. The problem I have now is that the drives are not one giant disk so I have to duplicate shares on each volume (i.e. D:\Share1, E:\Share1, etc.).

Apparently extending a volume across multiple disks in Server 2008 is dangerous in that if one disk fails, the entire volume is done for. So it seems that RAID 5 could be a good solution to this problem. Furthermore, I would like to keep transfer speeds as fast as possible since the data on these disks is often streaming to another device, etc.

My questions are the following:

  • What is the "optimal" number of drives to have in a RAID 5 array? Should I just buy one more 1TB drive? What if I have 4 1TB drives?

  • Does the number of drives in the RAID5 array affect the transfer speed? I'm assuming that RAID 5 is still faster than my current configuration (single volumes)

  • With a RAID 5 array, does it matter how many partitions you create on the array?

Thanks in advance for your advice!

P.S. all data is backed up to another device.

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2 Answers 2

What is the "optimal" number of drives to have in a RAID 5 array? Should I just buy one more 1TB drive? What if I have 4 1TB drives?

Optimal number is typically 3 disks. If you have 4, you can use 1 for a hot spare which is recommended should a drive fail. Once a disk fails you need to quickly rebuild the bad disk from parity as the longer it goes hobbled, the probability of another disk failure increases.

Does the number of drives in the RAID5 array affect the transfer speed? I'm assuming that RAID 5 is still faster than my current configuration (single volumes)

Number of drives doesn't usually affect the overall transfer speed. What you really need to know is that RAID 5 is typically read speed is very good, write speed is slow. If this meets your needs stick with RAID 5.

With a RAID 5 array, does it matter how many partitions you create on the array?

I honestly don't know if partitions and arrays affect performance and what not. I try to make it a 1:1 ratio but if you need to slice the array, I'm unaware of any major possible hangups/issues.


I am planning on setting up a RAID 5 array on my data storage drives using Windows Server 2008 software RAID

I highly recommend avoiding software RAID especially for windows. And onboard "hardware" RAID for Intel/nVidia or whatever. If you're really serious about RAID for data protection, get a real hardware card from a reputable vendor (3Ware, LSI, Adaptec, etc.). Some argue that Linux software RAID is relatively safe and effective but Windows software RAID (AFAIK) has never really a solid reputation. In my experience, hardware RAID is the way to go if you really want to have any peace of mind in terms of data protection.

P.S. Even though your data is backed up to another device do you really want to go through the headache of rebuilding a software RAID array if it can be avoided for some $$$? Also, if you really want some level of protection, I'd highly recommend running (hardware) RAID 6 as it can sustain a 2 disk failure where as RAID 5 can only handle 1 disk failure.

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"Optimal number is typically 3 disks"? This is just usually the minimum. It really depends on what you are trying to optimize. Based on how the parity works there are specific optimal number of drives, but I'm having trouble finding it. It was either 5, 9, 13, or 3, 7, 15... or something like that.. spent 30 minutes looking for the article, but turned up nothing. –  Jarvin Jun 29 '10 at 17:02
    
I heard software RAID-5 in Windows actually wasn't that bad? I really don't have the money to buy a separate hardware RAID card. I don't really mind if the performance of software RAID is slower, as long as it is faster than individual drives... –  Nitax Jun 29 '10 at 17:19
    
Performance wise, software RAID may be on par or better. I don't know as I've stayed away from it for years. As far as reliability/stability, I trust hardware RAID 1000x more than software RAID. In your case, if software RAID is the only option, RAID 5 would probably be best. How do you plan to use your Win2k8 server? –  osij2is Jun 29 '10 at 19:35
    
It is primarily going to be a file share / backup tool. A few drives will host media that will be streamed to various devices on the network. It will also host a VPN that will allow me to access files on the go and maybe even an FTP (if I can figure out how to get SSL working) for others to grab files. –  Nitax Jun 30 '10 at 16:20
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Also, the number of drives in the array DOES most certainly affect transfer speed. More drives = faster. –  MDMarra Aug 6 '10 at 19:20

What is the "optimal" number of drives to have in a RAID 5 array? Should I just buy one more 1TB drive? What if I have 4 1TB drives?

Optimal is a variable number. What are you looking for - read performance, write performance, rapid rebuilds, minimum wasted space?

I've built RAID 5 arrays in chunks from 4 disks to 24 disks as a single unit. Each has had advantages and disadvantages. Larger units waste less space, but take longer to rebuild and have a higher write overhead.

Does the number of drives in the RAID5 array affect the transfer speed? I'm assuming that RAID 5 is still faster than my current configuration (single volumes)

Yes, with caveats. Up until a certain limit (which is defined by your hardware and configuration) adding more disks will increase the maximum read speed, and reduce the maximum write speed. Whether you'll actually notice it depends on the workloads.

Things that influence it include the number of controllers, characteristics of the disks and controllers etc.

With a RAID 5 array, does it matter how many partitions you create on the array?

Depends on how you'll be using it really, in practice probably not.

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