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RAID5 Array.. Anyone?

S

subscience

Gawd
Joined
Aug 10, 2002
Messages
946
Hey guys, glad to see [H] back up and running.

I am seriously considering setting up a RAID5 array in my next rig. Does anyone have any first hand experiece with this? And does anyone know if there are any SATA RAID controllers with RAID5 capability? Or should I stick with SCSI in this case? I'm fairly new to the RAID arena (sans the simple on board RAID0 stuff), so I'd love to hear from you veterans.

Thanks. :)
 
RAID5 is not something I'd want in either a desktop or workstation, it just writes too damn slow, increases access times (big killer for me) and uses too much space/power. There are SATA RAID5 controllers, but they're running about $100 over PATA equivalents, which is pretty close to SCSI prices. SCSI drives are also firmware tuned to work with RAID better than SATA, so they do have a bit of an edge in certain acccess patterns. All in all, consider using a fast SCSI disk or two in your desktop, then put a RAID5 in a network server for mass file storage.
 
The quick answer....
Yes, to experience. Raid 5 rocks. it's great for server environments, but expect a performance decrease from raid0. I actually looked ealier today for cards to do raid5 with sata, and newegg carries a few of them (sorry didn't take not of links when browsing)

Anyway, what is your reason for going 5? If you want performance and redundancy you could go 0+1.

In favor of raid 5 if you're running a lot of discs, and want to be covered if one dies, then that is the way to go, but for most home applications (even the [H]ardest of them it's likely to be overkill) and quite expensive. you'll need to run at least 3 drives, preferably 5 (may as well make the striping work for you.

Likely you'll really only see the fun, if durring the middle of doing something you pull a drive out and pop in a hotspare and let it rebuild (it is cool technology)

If data recovery is your main key. go for raid 0+1, or just 0 and a good DLT backup system.

-Jeff
 
Ah. Good to know guys. So RAID5 is a no-go for your day-to-day desktop environments. Looks like I'll be sticking to RAID0 then. Maybe RAID0+1.
 
Not to be anal, but keep in mind that 0+1 takes a lot more storage space than
you actually get out of it.

say for example 4 250gig drives
first create two raid0 sets of 500 each
then create a raid1 set of 500 from the total of 1000 that you have in your box.

The upshot is that if a drive fails, there is a mirror in existance to rebuild it.


it's expensive, but if you've got the money, it's nice
I wish I had the money.

do some google searching on raid levels, you'll get a better understanding, and probably find the right set of tradeoffs (everything involves tradeoffs) that work for you.

-Jeff
 
Well Id disagree, but then its really a matter of the roll your asking a desktop\workstation to play

Ive been running a Promise SX6000 PATA RAID 5 array in a workstation for 3 years
but Im not writing to it from an ap, its simply my archive and it just happens to be Direct Attached Storage (when veiwed locally, its a NAS when viewed from my current workstation :p )

there are also some good things Im hearing about NetCell's SynchRAID > (Download the SynchRAID Removing RAID Adapter Bottlenecks Whitepaper)
but its really optimized for a certain access pattern (large files like in video editing)
and would suck for say a database access pattern

Snugglebear is right about the heat and power issue, definately something that needs to be addressed (and there is no delayed spinup option like you get in most SCSI arrays) it "tests" power supplies, I ran synchd 400watts when I first got it (there where then 12 HDDs + 2 opticals), switched over to a Zippy N+1 650w redundant when i picked up a Rackmount off ebay (with then fewer drives), far overpowered in both cases, but thats not necessarilly a bad thing ;)

It also has 128MB buffer and a dedicated RISC processor for parity calculations
so the performance isnt so bad, but nothing compared to a single HDD
 
XOR calculations appear to require a decent chunk of CPU time, so much so that you may want to have a look at this article using an afforable Highpoint "soft" RAID 5 system. It also appears that soft-L5 solutions perform better depending on platform, as seen in the follow-up article.

This section of the conclusion from the latter article is notable:
The first thing that needs to be mentioned is that all 32bit platforms suffered from artifacts in the form of mouse-lag, and a bit of choppyness with the Level5 RAID setup. We mentioned this in our original review already, likewise, we mentioned the issues of USB vs. PS/2 mouse along with our suspicions that some of this may relate to drivers operating at a "current privilege level" (CPL) of 0 or 1 (Kernel or superuser level) that allows the controller to take control of all system resources as needed, abeit at the expense of other applications running.

This is where the Athlon64 was in a league of its own, there were no lags, there was no choppyness, the system was all business as usual and showed the crispness we were missing from the P4 and, to a lesser degree, from the AthlonXP platform. We won't go into too much speculation here but aside from the raw write performance, the Athlon64 platforms really breezed through the benchmarks run here and the excess of performance of the CPU may be a reason why we did not see any starvation of other devices to the level where it would become noticeable to the user.
Click to expand...

It certainly looks to me like anyone really desiring RAID5 and good performance should buy a controller with a dedicated XOR processor rather than a less expensive solution like the RocketRAID 1640. RAIDCore or Promise might offer such a beast in SATA flavor, but I'm not sure.
 
i plan on using a RAID5 array when i build my HTPC...probably something like five 200GB drives....gonna use it for making copies of all my DVD's directly onto the hard drive so that I don't have to get up to change discs when i want to change movies...just have them all archived on the RAID storage center, and if one drive fails, it will be able to recreate the data, and i don't have to re-rip the DVD's again :D
 
Ice Czar,

I'm not saying he shouldn't run a raid 5 array, I'm simply trying to make sure that he knows
what he's getting into before getting into it. RAID 5 is great, but in my opinion not worth the setup if you're running less than 1T at 1.5-2T it becomes a more realistic option.

Hardware controllers are the only way to go, and if you've got the budget a full on SAN device would be ideal. I am assuming that most of us on this board are doing a lot of this for the sheer fun and geekieness of it. (I don't consider geek a dirty word, so if you do, Tough!)

Since you're using it for archives you're obviously coming from the right direction. raid5 as a boot and/or swap/page would not be a great performer.

I think the person who mentioned using 5 in a htpc has a great idea. I was going to build one going for as small of a formfactor as I could manage, but now I might have some rethinking to do.

-Jeff
just overinflating the value of my $.02
 
I have a RAID5 array for my server, using eleven 36GB SCSI disks for a 324GB redundant array + hot spare. For some data saftey on the desktop I'd look into RAID1 and save the heavy duty setup for a backup server.
 
JeffS said:
I think the person who mentioned using 5 in a htpc has a great idea. I was going to build one going for as small of a formfactor as I could manage, but now I might have some rethinking to do.
Click to expand...

Network servers are really easy to setup and manage, and put that disk overhead somewhere else. This allows you to use smaller form factors on your clients, along with smaller PSUs and cooling systems, while maintaining access to the data from the other machines. For media playback all you need is 802.11G or 10base, for encoding and mass transfers, stick to wired 100base or possibly gigabit. I went the server route years ago when I finally replaced the old Dell from undergrad and made that into my server and wouldn't do it any other way. Certainly makes things easy considering the number of machines and platforms I'm running.
 
Snugglebear said:
...For media playback all you need is 802.11G or 10base, for encoding and mass transfers, stick to wired 100base or possibly gigabit....
Click to expand...

i would recommend against using 10base for that unless you are the only one who will be playing back anything over the network, and you don't plan on doing anything else over the network at the same time (especially if you are playing back archived DVD's or other types of medium- to high-bitrate video). there are several reasons i say this:

1) if kids/friends/roommates/etc. also use it at the same time, playback could suffer.
2) 100base or 802.11G is cheap enough that it doesn't make sense to buy a slower network card.
3) even if you are the only one using it now, who's to say you won't be in a situation later where there are multiple users accessing it simultaneously?

the only reason i could see for using 10base is if you already have the hardware and it is the only hardware you can spare without buying more, or if you are just absolutely dead-set on putting that 10base card to use. even so, you can get 100base for like $5 - $10 per card.....
 
just for the record, i've got software raid 5 through 16 seagate elites - at absolutely max proc usage (rebuilding the array), i used 20% of the processor on a p3 500 - normal read/write usage was about 12% - you don't have to have a card to do it succesfully, and i like having all of the software options available to me
 
In Windows? or Linux

its also dependent on the access pattern
 
i'm using a promise sx4000 with 4x160GB Maxtor PATA drives. The write time is good, the access time is great.

I only wish I could use 5 drives with this controller.
 
86reddawg said:
linux, or course :p
Click to expand...

well, thats cheating :p

Linux is far better in software RAID from what I understand


the SX4000, came out right after I got my SX6000 (and I immediately wanted it)
you running it at 33 or 66MHz?
did you stuff in the full 256MB for the cache?
 
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