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cheap raid 5 array?

M

MonsterMac

n00b
Joined
Dec 27, 2005
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27
is there such thing as putting together a cheap raid 5 array? I'd like an 8 drive array or so, I think i've found my card (3ware SATA Raid-5 one, either PCI or PCI-X depending on the motherboard I get) and my drives (WD3200JD's) but i'm not sure about motherboard/cpu/ram. i'd like to get max transfer speeds (100mbit) for one or two users at once (most of the time just one). Any ideas?
 
for the cheapest of cheap, you can run software Raid 5 in windows, just do a google search, will even do pairity/reconstruction. Doesnt have any kind of online expansion options, but no biggie.

Software raid 5 should beable to saturate 100mbit with little issue, my LSI hardware Raid 5 goes about 20MB/s over gigabit network, so im sure software could at least hit 10MB/s(12.5MB/s max in theory for 100mbs).

Other than that, you'll be looking at any number of hardware controllers.
 
I'm going through the same thing myself. I spent a while trying to figure out what kind of processor power would be needed for such a rig... so I'll pass along a bit of the stuff I learned along the way.

Basically, for CPU/RAM/mobo you first have to figure out what you're going to be using the system for. With RAID controllers made by companies like 3ware and Areca, they have their own onboard I/O processors to remove that duty from the system CPU, so very few CPU cycles are spent actually reading and writing to the RAID array. If you're only planning on using the system for serving files or sharing drive space and nothing more and have a lightweight OS in mind (like Linux, or BSD), then you can get away with a very minimal CPU and a basic mobo and a modest amount of memory and still realize full throughput on your RAID array. However, once you add or change the projected role of the system to include other servers or applications, or if you choose to run a Windows server product as your OS, you may have to ramp up your CPU and RAM accordingly.... but all in all, the file serving part is NOT processor intensive at all. In my case, I'm going to use Linux with Samba to power my file server box equipped with an Areca ARC-1130 PCI-X controller. To power the whole thing, I've decided on a plain P4 running on a basic server motherboard most likely with 512 MB or more of ECC RAM.

A few notes when choosing a mobo..... your choice of which interface you will use sorta dictates what kind of mobo you will need. If you choose PCI, you can probably run it on anything with a PCI slot on it. If you choose PCI-X, you are pretty much limiting yourself to using a server motherboard since PCI-X slots seem to exist only on server/workstation boards. Of course, should you go the PCI-X route, make sure you're choosing a board that fully supports the RAID controller you choose. The cards from both 3ware and Areca call for a 64bit/133MHz PCI-X slot and I have found out through my searches that there is only a subset of server boards that actually have one or more of these slots. If you're looking for a fast transfer rate, you'd probably best use PCI-X. Besides that, it appears if you want to use SATA-2 drives you'll have to choose a PCI-X based controller (or better... Areca makes a PCI-E controller as well). As I am told, even 8 drives on the same controller going full tilt couldn't fill up the bandwidth provided by a PCI-X bus, so moving up to PCI-E thinking you'll get better throughput might not gain you anything except a different batch of choices to choose from when it comes to motherboards.

However, no matter which interface you choose, you'd be better off using a server mobo anyway. You get quite a few other benefits this way... like the ability to use ECC RAM, usually a larger max memory capacity, as well as a lot of built in stuff like onboard video and one or more LAN ports (many with Gb LAN controllers). I did a bit of thinking about it myself... my first idea was to use a regular mobo to power my file server, but then I figured I'm putting in this expensive RAID controller and a large number of drives (also expensive) so I can have some sort of peace of mind knowing I have a somewhat stable, yet high capacity storage medium. So, why screw it up by using a desktop motherboard and regular RAM (because ECC support is almost limited to server boards as well) that could potentially cause the data being stored to have errors? Besides, server boards aren't THAT much more than a regular desktop board.

Well, hope that helps a bit.
 
If you choose PCI-X, you are pretty much limiting yourself to using a server motherboard since PCI-X slots seem to exist only on server/workstation boards.
Click to expand...

PCI-X cards are backwards compatible with std PCI slots, they have some over hand when installed, but for most boards it's not an issue. Yes, I have run a pci-x card in a std pci-slot. A dell branded pci-x133 adaptec scsi controller on an asus p2b-ds.

The only downside to running pci-x on pci is the bandwidth limitations, with 8 drives, are going to be reached very quickly for the pci bus. If you're mainly transfering over a 100mbit network, it's not a big deal, but if you're planning on using the machine locally as well it could prove an issue.
 
Of course, IMO, if you're going to spend a significant amount of money purchasing a PCI-X RAID controller just to use it in a PCI slot, it might be more worth your while to purchase a PCI-E RAID controller for a few more bucks in order to use it in a PCI-E slot (which a lot of current desktop boards have one or more of). At least then the interface would not be a speed bottleneck and you would be able to take advantage of the full speed of your RAID array. All you'd have to make sure of though is that it's the correct kind of PCI-E slot (the ones made by Areca are PCI-E 8x for example... I'm not familiar with any other PCI-E based controllers though they may exist).
 
Also, keep in mind that PCI-X slots are only backwards compatable with 5v (two notches) and not 3.3v cards (one notch).
 
Joe Fission said:
So, why screw it up by using a desktop motherboard and regular RAM (because ECC support is almost limited to server boards as well) that could potentially cause the data being stored to have errors?
Click to expand...
ECC becomes more useful the more RAM you have...but a file server uses very little RAM. And in any case, ECC is primarily for system stability...while its possible a stray gamma ray burst would cause non-ECC memory to corrupt a file being written, its not that likely. Buy ECC if you want, but I've seen non-ECC file servers run 10 years without needing so much as a reboot.
 
A supermicro AOC-SAT2-MV8 with software raid (windows server OSs or Linux) will get you decent speeds, and only around $130 for it. It's 3.3 and 5v compatible.

If you use Western Digital drives on Windows, I'd recommend Raid Edition drives.

 
One note is that those WD drives are known for RAID issues as they are not the RAID edition drives...

This means they can be in recovery mode for up to 30 seconds (trying to correct an error) and this is long enough to cause the RAID card to think they have gone bad and to drop them from the array...

Personaly I like WD drives, but don't use non RE WD drives in a RAID array.

==>Lazn
 
The non-raid edition drives suffer from an error recovery bug where when the drive encounters an error, it goes into recovery mode and doesn't respond to signals from the outside world. The RE drives have a TLER (time limited error recovery) feature wherein they'll only try to recover for 8 seconds and then give up.

The advantage of this is that a raid controller would see a non-RE drive's lack of responses as a bad drive, and drop it from the array. Then when the drive finishes doing its thing, the controller notices it's missing and adds it back to the array. So you end up doing an array rebuild when it's not necessary, and while the rebuild is happening you have no redundancy. RE drives come back to a responding state fast enough that they don't get dropped in the first place, preventing the problem.

 
The bad reviews are because Newegg doesn't ship drives properly. Order from ZipZoomFly and you won't have problems.

 
masher said:
ECC becomes more useful the more RAM you have...but a file server uses very little RAM. And in any case, ECC is primarily for system stability...while its possible a stray gamma ray burst would cause non-ECC memory to corrupt a file being written, its not that likely. Buy ECC if you want, but I've seen non-ECC file servers run 10 years without needing so much as a reboot.
Click to expand...
Point noted.
 
MonsterMac said:
what makes you say that? i've ordered a lot of my drives from newegg... no problems so far? is this a known issue, this is the first i've herad of it.
Click to expand...

Well known issue here on the [H]... They come wrapped in bubble wrap or in peanuts and other than that just the bare drive in static wrap.. so they can work there way to one side and have just one layer of cardboard protecting them. If they don't get shaken too much they are fine.. but far too often people have gotten DOA drives from newegg because of their packing materials.

I am a huge fan of NewEgg, but I do not buy hard drives from them.

==>Lazn
 
Alright, I will keep that in mind for all my future hard drive orders. If I were to put a 4 drive raid 5 array in my computer with that 3ware raid controller mentioned above (the 4 raided hard drives would be WD 400GB RE SATA) in my main pc (used for gaming - I have A64 3200+ Venice core, 6600GT, 1gig of ram (soon to be two, also possibly an upgraded videocard), and I play to put the os on a 74gb WD Raptor 10k drive. Would my games play any slower, or not as fast, with a raid in my only rig I use for everything, during any specific times (i.e. when surfing the web, in games, writing things to the drive(s), etc.)?
 
MonsterMac said:
Alright, I will keep that in mind for all my future hard drive orders. If I were to put a 4 drive raid 5 array in my computer with that 3ware raid controller mentioned above (the 4 raided hard drives would be WD 400GB RE SATA) in my main pc (used for gaming - I have A64 3200+ Venice core, 6600GT, 1gig of ram (soon to be two, also possibly an upgraded videocard), and I play to put the os on a 74gb WD Raptor 10k drive. Would my games play any slower, or not as fast, with a raid in my only rig I use for everything, during any specific times (i.e. when surfing the web, in games, writing things to the drive(s), etc.)?
Click to expand...

In every day use, with that 3ware card, I doubt you would notice. It will read fast (so loading games will be fine) it is just large writes that will notice a slowdown..

Xbit-labs has a review of the 8 port verson of this card: http://www.xbitlabs.com/articles/storage/display/3ware-8506-8.html

==>Lazn
 
Lazn_Work said:
In every day use, with that 3ware card, I doubt you would notice. It will read fast (so loading games will be fine) it is just large writes that will notice a slowdown..

Xbit-labs has a review of the 8 port verson of this card: http://www.xbitlabs.com/articles/storage/display/3ware-8506-8.html

==>Lazn
Click to expand...

a slow down as in my whole processor being used, and everything on my computer will be slow? or do you mean stuff will write 'slow' to the array itself?
 
MonsterMac said:
a slow down as in my whole processor being used, and everything on my computer will be slow? or do you mean stuff will write 'slow' to the array itself?
Click to expand...

Just writing to the array itself. It will not slow down your whole computer.

==>Lazn
 
how slow do you think it would write? any ideas? a lot slower than a regular 7200rpm/8 or 7200rpm/16mb cache drive?
 
http://www.gamepc.com/labs/view_content.asp?id=r52005&page=12&cookie_test=1

"Write speed is another issue altogether. RAID-5 is intensive when writing data, as the actual data along with parity information is written to each drive in the array. Typically, write speeds will be roughly one fourth those of read speeds. Our RAID-5 cards show huge differences in Disk Write speed though. The only card which is able to maintain excellent disk write speeds is the RAIDCore BC4452, which held strong at 65 MB/s write speed. In comparison, the Silicon Image and 3Ware controllers give fairly abysmal write speeds, ranging from 5 MB/s to 15 MB/s."

==>Lazn
 
My raid 5 in Linux gives ~50MB/s writes when DMA's on. Individual drives get ~60. Not sure why it's so slow - full stripe writes should be about (N-1)*S MB/s, where N is number of disks and S is speed of single drive. Maybe when I add another drive I can give everyone an update.

 
unhappy_mage said:
My raid 5 in Linux gives ~50MB/s writes when DMA's on. Individual drives get ~60. Not sure why it's so slow - full stripe writes should be about (N-1)*S MB/s, where N is number of disks and S is speed of single drive. Maybe when I add another drive I can give everyone an update.

Click to expand...

How do you figure? Raid 5 writes are slow because there has to be a parity caluclation done for every write. Reads don't have this penalty because the parity bit only gets checked if a drive has failed. So that calculation will work for read burst speed, but not write speeds.

==>Lazn
 
ok, thanks for the info, just to confirm - it will be slow when writing the data (no big deal, just a storage drive to hold back ups and stuff like that, mp3's, dvd back ups, pictures, etc. but will not slow my computer down at all (it is hardware raid-5).
 
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