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Rob Williams 09-23-2012 10:19 PM

SysAdmin Corner: Demystifying RAID
 
Interested in RAID, but not sure which option is right for you? The goal of this article is to clear up any confusion you may have. We discuss what RAID is, what it isn't, potential dangers, differences between popular RAID levels and last but not least, what you need to get yourself up and running with your very own RAID.

Read through Brett's in-depth look at all things RAID and then discuss the article here!

RainMotorsports 09-24-2012 04:24 AM

Very nice article. Had some plans for multiple arrays in this machine but hard drive prices went up and I am only getting caught up on that now.

My first raid was actually with my laptop. I was gifted an identical drive to the one that came with it by tech support for GenTechPC for representing them to potential clients. The higher end model of my laptop came from the factory in that configuration. In a perfect world I would have run RAID 1 but I could not afford drives big enough to actually enjoy that.

My second and current use is those same 2.5 inch 7200 RPM 320 GB drives out of the laptop in my desktop as a record array for fraps. Given a file the average speed needed for 1080P 60 fps is 68 MB/s but the 1500 Mbps of the codec suggest it could peak well over twice that at speeds a SATA II SSD would handle nicely. Lossless? Forget it I need an SSD :p

lferrante 09-24-2012 07:09 PM

Nice article. Two things I'd like to mention. One is that I hope you can add something about software RAIDs and their incorporations across different OSs and most impotantly what happens when the OS needs rebuilt, or the disks get transferred to another PC etc.

Second, I've been working with RAIDs in our office for years now on Dell PowerEdge machines and needed to benchmark a RAID50 vs a RAID10 and found that RAID10 is vastly superior except a hardly notable difference in CPU usage that could be completely unrelated. The short benchmark and details are posted here.

http://professorjunkdrawer.blogspot....benchmark.html

Kayden 09-25-2012 06:46 AM

Nicely done Brett!

I would point out that if your Steam RAID does go down like you suggest, you will lose you screenshots and any save games that you disabled cloud save on. I had that happen to a drive I had dedicated to Steam and I couldn't get that info back. It wasn't a major deal for or the majority of users, but could be a problem for others.

Brett Thomas 09-25-2012 09:50 AM

Quote:

Originally Posted by lferrante (Post 59210)
Nice article. Two things I'd like to mention. One is that I hope you can add something about software RAIDs and their incorporations across different OSs and most impotantly what happens when the OS needs rebuilt, or the disks get transferred to another PC etc.

Second, I've been working with RAIDs in our office for years now on Dell PowerEdge machines and needed to benchmark a RAID50 vs a RAID10 and found that RAID10 is vastly superior except a hardly notable difference in CPU usage that could be completely unrelated. The short benchmark and details are posted here.

http://professorjunkdrawer.blogspot....benchmark.html

Welcome, lferrante! I'm glad you enjoyed the article.

I planned to follow up with the discussion on software RAID in my covering of building a simple MDADM RAID5 array...so stay tuned, and hopefully you will find what you're looking for there. I've found that on Linux, software is vastly superior (as mentioned in my article), as it does not require rebuilding at all between OS changes. Windows, I'll have to do some research - the addition of RAID 0/1 in Windows is a nice one but I've not tested re-installs of the OS. I would, however, assume that to be fairly transparent - the encoding is part of the volume header's "Superblock" and should be visible to any Windows version that supports RAID, with no rebuilding required.

As far as speed tests - thank you for the link! RAID10 should ALWAYS be faster than RAID5/6, as there is no need to calculate a parity block. However, its sub-optimal use of disk space and arguably lower fault tolerance vs RAID6 on any array larger than four disks makes it a difficult balance. I've found a well-tuned RAID5 can more than supply a small office or (far more demanding) home theater setup! In the end, the choice between solutions at that level comes down to application goals - a big portion of what will determine a good setup involves WHAT you're serving (file size wise) and to how many users.

Brett Thomas 09-25-2012 09:52 AM

Quote:

Originally Posted by Kayden (Post 59232)
Nicely done Brett!

I would point out that if your Steam RAID does go down like you suggest, you will lose you screenshots and any save games that you disabled cloud save on. I had that happen to a drive I had dedicated to Steam and I couldn't get that info back. It wasn't a major deal for or the majority of users, but could be a problem for others.

Thanks, Kayden!

An excellent point. However, I *think* many users leave cloud saving on by default in Steam, and I don't know how many MAINTAIN a plethora of screenshots. But your point still rings true and hammers home the core of the concept - RAID is NOT a backup and RAID0 in particular is risky business that should only be used for things that can be replaced easily through other means!

Rob Williams 09-25-2012 12:48 PM

Quote:

Originally Posted by Kayden (Post 59232)
Nicely done Brett!

I would point out that if your Steam RAID does go down like you suggest, you will lose you screenshots and any save games that you disabled cloud save on. I had that happen to a drive I had dedicated to Steam and I couldn't get that info back. It wasn't a major deal for or the majority of users, but could be a problem for others.

And for those concerned about that, there's SyncBack!

http://techgage.com/article/using_sy...ndows_folders/

Of course it gets complicated if saved games are kept in the game folder rather than inside the userdata folder, but it's a good start. Most reasonable games save to Documents regardless.

For screenshots, I am sure I'm not like most people, but I use Fraps to capture the shots I want to keep for my personal collection, and Steam to capture only the shots I want to upload to the cloud.

SporadicMovemnt 09-26-2012 04:14 PM

Awesome article. I can't wait to see more in-depth articles in the SysAdmin Corner!

Rob Williams 09-26-2012 06:33 PM

Welcome to the forums, SporadicMovemnt, and thanks for the nice comments :-)

We're dreaming up some new ideas for SysAdmin Corner, so we hope to have more content up in the near-future. We're always up for suggestions as well if there's a particular interest.

Jakal 09-26-2012 11:23 PM

Really great and simplified write-up Brett. I already decided to go with a RAID setup with my in next build before you wrote this up. I was considering 3-4 SSDs in RAID for OS/apps, and using my current HDDs for misc files. I like the idea of RAID 0 for games though and will explore that option.

Thanks again for the great breakdown and review!

Rob Williams 09-27-2012 01:31 AM

If you're going to be RAIDing SSDs, I recommend avoiding 0 at all costs, even if it's just throw-away data. Some SSDs throw fits on random occasion that could screw you over. RAID 1 or higher would be fine.

Jakal 09-27-2012 04:06 AM

RAID 5 looks attractive. If I understand it correctly, you can achieve similar/better data transfer for game loading while still retaining redundancy.

Brett Thomas 09-27-2012 01:33 PM

Quote:

Originally Posted by Jakal (Post 59375)
RAID 5 looks attractive. If I understand it correctly, you can achieve similar/better data transfer for game loading while still retaining redundancy.

Absolutely! RAID5 is the performance "middle of the pack". On a 4-disk RAID5 array, I top out at about 290MB/s read speed with 5600RPM 2TB drives (a single drive on that system does a throughput of about 130MB/s). That's about 60% performance of what RAID0 would be but more than twice what a single drive would do. I wouldn't even BEGIN to imagine what you'd get out of three or four SSD's.

Keep in mind that the more "full" RAID5 gets, the slower it can get because of random seek/write speed issues involved in parity calculations...but that's something I'll touch on in the next SysAdmin corner. :)

However, I will say I'm not a fan of using anything but RAID1 for an OS drive...too many random reads/writes, small files, etc.


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