a little confused as to how raid works

raid0-distributes data between 2 discs and is not redundant
-disks can be different sizes but you lose half the storage capacity
-fast read/write times, loading of os

raid1-mirrors discs so the same info is on both
-space is limited to the smallest disc capacity (2 150gb hdd= 1 150gb hdd)

raid5-minimum of 3 discs
- storage capacity of array is reduced by 1


is this information from what ive read and interpreted correct?

or if i just wanted a drive specifically for the os and booting, i could get the 36gig raptor and then get another (or a couple) like 500gig for all my shit? would i need to set up a raid array for that situation? im thinking no but i just need some clarification

4/16/2008 5:41:29 PM

http://en.wikipedia.org/wiki/Redundant_array_of_independent_disks

/thread

4/16/2008 5:42:40 PM

yea thats what i was lookin at...

i didnt see if in raid0 you can use more than 2 hdds

also asking TWW who uses what array and why?

4/16/2008 5:46:10 PM

why?

either speed, redundancy, or both.

not sure about the raid 0 over 2 disk question but my quick googling says you can use over 2

somebody else will chime in though i'm sure

[Edited on April 16, 2008 at 5:53 PM. Reason : changed my mind]

4/16/2008 5:50:59 PM

raid 0 stripes your data across the drives in the array set. you can have drives of different sizes, but the size of the array will be determined by the size of the smallest disk multiplied by the number of disks. there is no fault tolerance, and for every disk that is added to the array, the risk of array failure doubles. not a good idea unless it's for data you don't particularly care about.

raid 1 mirrors your data on whatever drives are in the array. this is the level with the highest redundancy. more disks = more redundancy = less chance of catastrophic failure. the size of the array is determined by the size of the smallest disk in the array.

raid 5, without getting into too much detail, basically stripes your data across n - 1 of the drives (where n is the number of drives in the array) and uses the last drive in the array to store parity information. if one drive fails, you are still able to recover the information. insert a new drive, and the array will rebuild itself using the parity information. raid 5 can't handle more than one failure at a time, though.

there are other raid levels, some of which offer even greater redundancy.

personally, i use raid 5 for most arrays (both personally and at work). i've never encountered a situation in which two drives failed at once. it's either one of them, or all of them (as the drives usually come from the same manufacturing lot).

the general rule of thumb is that more redundancy = less storage space.

how's that?

4/16/2008 5:55:05 PM

Quote :

"i didnt see if in raid0 you can use more than 2 hdds"

Yes. The more disks the faster it will be and the larger your array can grow, but your chances of failure increase with each disk you add.

4/16/2008 7:50:55 PM

thanks guys, i understand it better now

^^ what kind of drives are you using? brand? capacity? motherboard?

4/16/2008 8:05:43 PM

most of the arrays we build are from either 146GB or 300GB SAS drives running off of a PERC. the drives are usually either seagate, fujitsu, or WD.

most of our powervaults are ultra320 scsi w/ 300GB drives connected to another PERC.

4/16/2008 11:10:16 PM

raid0 is only worth it if you have a place to actually back it up or don't care about the data.

raid5 is the way to go <= 12 disks. raid6 above that imo.

4/16/2008 11:47:55 PM

in raid5 does it matter if the drives are all the same size?

4/17/2008 12:23:00 AM

yup

4/17/2008 12:32:31 AM

^what kind of set up do you have?

4/17/2008 12:43:45 AM

It should be noted that for a long time, most consumer-level RAID controllers (either as cards or onboard motherboards) would only support RAID 0, RAID 1, and RAID 0+1.

When I built my last machine, I found that RAID controller cards with RAID 5 were several hundred dollars. What I ended up doing was having a mirrored partition of two 160 gig IDE drives, using a PCI RAID controller card, and having a striped partition of two 80 gig SATA drives. This setup served me well for a long time

[Edited on April 17, 2008 at 12:57 AM. Reason : .]

4/17/2008 12:45:13 AM

how about the newer mobos with raid support?

from wikipedia....

Quote :

"Operating system-based RAID cannot easily be used to protect the boot process and is generally impractical on desktop version of Windows (as described above). Hardware RAID controllers are expensive. To fill this gap cheap "RAID controllers" were introduced that do not contain a RAID controller chip, but simply a standard disk controller chip with special firmware and drivers. During early stage bootup the RAID is implemented by the firmware; when a protected-mode operating system such as a modern version of Linux or Microsoft Windows is loaded the drivers take over. These controllers are described by their manufacturers as RAID controllers, and it is rarely made clear to purchasers that the burden of RAID processing is borne by the host computer's central processing unit, not the RAID controller itself, thus introducing the afore-mentioned CPU overhead. Before their introduction a "RAID controller" implied that the controller did the processing, and the new type has become known in technically knowledgeable circles as "fake RAID" even though the RAID array itself is implemented correctly."

so would i need to get a raid controller via pci or whatever separately even if the motherboard has raid support in 0/1/0+1/5?

4/17/2008 12:52:59 AM

One of the nice things about having a controller card though, is that you can leave all the drives plugged into it, and move the controller from machine to machine without losing the partition.

[Edited on April 17, 2008 at 1:04 AM. Reason : .]

4/17/2008 1:03:07 AM

any suggestions on a controller card?

4/17/2008 1:12:38 AM

^ What's your budget and intended use?

4/17/2008 1:46:58 AM

Quote :

"What's your budget and intended use?"

this is important.

you have many options.

for instance, the PERC cards i use run upwards of several hundreds of dollars.

4/17/2008 1:49:01 AM

holy sh!t. i had no idea those things would cost that much (just browsed on newegg)

something like this would be fine i think
http://www.newegg.com/Product/Product.aspx?Item=N82E16816115029

or this...
http://www.newegg.com/Product/Product.aspx?Item=N82E16816102062

with 4 internal connectors that should be all i need to run raid5 yea? or for that matter, any raid array with < = 4 sata hdds?

4/17/2008 2:19:32 AM

both of those cards are fake RAID controllers

obviously it's going to be slower


not sure what your particular application is, but you may want to take that into consideration

4/17/2008 5:29:16 AM

what would you recommend at a fairly cheap price? <$250

4/17/2008 9:08:48 AM

At that price you may be able to get a dat72 drive and backup your important shit to tape. You're certainly not going to be able to get any decent raid setup for that price, and only small(ish) capacity tape solutions.

4/17/2008 9:28:20 AM

Tape backup solutions are no longer cost effective unless you already own the equipment.

4/17/2008 9:34:30 AM

Hence why an older dat72 off ebay may be in that price range.

4/17/2008 9:37:13 AM

I'd rather rsync to a NAS appliance.

4/17/2008 9:49:45 AM

For less than $250?

4/17/2008 9:53:12 AM

Quote :

"raid 5, without getting into too much detail, basically stripes your data across n - 1 of the drives (where n is the number of drives in the array) and uses the last drive in the array to store parity information. "

not to nitpick, but this description is false. RAID5 spreads parity across all of the disks in the array. The parity is structured in a way that any one disk in the array can fail and there is no data loss.

RAID4 works as you described, with a dedicated parity disk. RAID6 is similar to RAID5 except you can lose 2 disks and still survive (but you have less usable storage).


If you want to buy a "real" RAID card, check out the Adaptec 3405. It supports 4 disks, SAS or SATA. we have several of them in use and they work well. I think they are sometimes under $300 on newegg.

4/17/2008 11:13:25 AM

1. on a board with raid support (0,1,0+1,5,etc.) do i need a raid controller as well?

2. other than being slower than a "real" raid controller, is there anything else performance-wise comparing it to a "fake" one?

3. if i just said forget the raid and got a raptor for my bootdrive and like a bigger drive for all my shit, i wouldn't have to set up anything special or partition anything, etc., correct? just plug and play?

4/17/2008 8:40:59 PM

Unless you really had some pressing legitimate need for an array, I was going to suggest you just go with ^#3 there to begin with.

That's a damn simple solution that would work well for all you probably intend to do, and it's much cheaper than investing in a RAID controller. Unless you truly need some kind of HA or redundancy/fault tolerance, there's no reason to invest in that kind of equipment. Basically, if you're not familiar with RAID or you're not hiring someone to do this, chances are, you don't *really* need it.

[Edited on April 17, 2008 at 8:56 PM. Reason : .]

4/17/2008 8:54:32 PM

haha i mean the only reason i was considering it was cause i asked myself, why not?

but yea i really never have backed up my shit in my gateway home pc nor my own dell laptop so i obviously wouldnt lose sleep over not having an array, it was just a thought cause im trying to get into this pc building thing.

i tend to get carried away with stuff i dont really "need." hell, i dont "need" a raptor to speed up my boot time or programs/games, but i might as well so i dont get mad and break anything

4/17/2008 9:06:24 PM

It's just not a worthwhile investment if you don't need it, so go with the high-rpm drive for OS and a slower archive drive for data. It will provide a decent increase in performance for much less money.

4/17/2008 9:15:59 PM

yea i have the option of an array if i ever feel like it in the future so im not worried about it too much anymore

i just want to get my shit set up!!!

4/17/2008 9:20:10 PM

yea you might want to check out a NAS appliance like Drobo.com, newegg sells them.

having your data protected by RAID is still not a replacement for backups. you can still suffer from accidental deletion, virus, corruption or a RAID controller failure.

4/18/2008 8:56:34 AM

Well to be honest, software raid really isn't that bad for the casual user. Everyone knows disk IO is one of the biggest bottlenecks. My load-times in games are incredibly fast, and I boot in under 45 seconds.

4/18/2008 9:31:26 AM

i bought a 12 bay sata -> scsi raid system for $550 and sold all the 250gb drives in it for $45 each so got it for free. slapped in 750gb drives and the thing rocks

had 2tb issues so just made 2tb logical volumes and used LVM in linux to put them together.

i've got another pc case with 8 drives in it with a highpoint raid5 card that has worked just fine. the western digital drives in it suck, but seem fine after the first few died.

the other 20 drives are all seagate.

4/18/2008 10:53:55 AM

You must have a lot of porn.

4/18/2008 10:55:12 AM

^^holy shit.

i remember when my family got our gateway for the house like 5 years ago. 2 60gig hdds and i was like

now its like dude who doesnt have at least half a terabyte of storage space?? fuckin SKANKS!!!

[Edited on April 18, 2008 at 11:10 AM. Reason : ^]

4/18/2008 11:09:47 AM

HD video editing for the win!

4/18/2008 11:55:29 AM

Quote :

"had 2tb issues so just made 2tb logical volumes and used LVM in linux to put them together."

fdisk can't handle >2TB partitions. Just use parted

4/18/2008 1:15:38 PM

it was scsi issues.

i had to use parted for the 8tb LVM anyways

4/18/2008 1:37:51 PM

I'm currently using five 300GB SATA drives in RAID 5 for mass storage and two 72GB Raptors in RAID 0 as an OS/programs drive on my main desktop.

Rather than bother with a dedicated RAID card I used these instructions to enable software RAID 5 under XP Pro. While the performance isn't that of a dedicated hardware solution, its a hell of a lot cheaper and more than good enough for my video stockpiling.

4/18/2008 11:16:26 PM

haha, we've got almost the same setup carl

2 76gb ultra320 drives in raid1 for the OS (currently vmware ESX 3.5 w/ w2k8, fedora, and openfiler guest VMs)

4 300gb ultra320 drives in raid5 partitioned into 3 iscsi targets of varying sizes

my macs back up to them via time machine, and i use the largest one as a data repository for all my machines

'tis nice

4/19/2008 12:16:01 AM