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AuthorTopic: Any Raid Experts?  (Read 3836 times)

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Offline trekiej

Any Raid Experts?
« on: June 24, 2010, 04:20:51 AM »
I am planning to build a new computer and I wanted to get some advice on Raid5 and Raid 1+0.
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Offline Jope

Re: Any Raid Experts?
« Reply #1 on: June 24, 2010, 06:50:00 AM »
Quote from: trekiej;566867
I am planning to build a new computer and I wanted to get some advice on Raid5 and Raid 1+0.


My advice to you:

RAID is for availability, not continuity. No matter which solution you select, make regular backups of all the data you can't afford to lose.

If you have enough money, get a hardware RAID board. You can tell by the fact that they are expensive. ;-)
 

Offline Piru

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Re: Any Raid Experts?
« Reply #2 on: June 24, 2010, 07:03:35 AM »
Quote from: trekiej;566867
I am planning to build a new computer and I wanted to get some advice on Raid5 and Raid 1+0.
Personally I use a large NAS (4 x 1.5TB HDD) and a server (3 x 1.5TB) RAID-5 setups to store data. My desktop machines have only relatively small SSD HDDs. The NAS/server storage is available to all my computers in my home LAN.

If you're going to use large capacity drives, use RAID-6 rather than RAID-5. I already am pushing it with RAID-5 containing 4 1.5TB HDDs. If one of those HDDs should fail, it already is quite likely that 2nd one fails during the rebuild.

Also, as already mentioned RAID itself doesn't replace backups. So remember to backup our important data even when using RAID.
 

Offline ElPolloDiabl

Re: Any Raid Experts?
« Reply #3 on: June 24, 2010, 07:23:33 AM »
I'm planning to have a striped main drive and then another drive as manual back up. The most likely problem would be a virus corrupting the drive and it doesn't seem very safe to have everything split in two.
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Offline sknight

Re: Any Raid Experts?
« Reply #4 on: June 24, 2010, 07:28:38 AM »
Quote from: trekiej;566867
I am planning to build a new computer and I wanted to get some advice on Raid5 and Raid 1+0.


Raid doesn't guarantee your data integrity. It doesn't detect silent data corruption for instance.
At present the best solution to preserve your data is to use ZFS as filesystem. It's available for Solaris, OpenSolaris, FreeBSD and Linux (in user space only - kernel module version still under development).

To have an idea of ZFS benefits take a look at this article: http://constantin.glez.de/blog/2010/01/home-server-raid-greed-and-why-mirroring-still-best

There are a lot of other interesting documents about ZFS on the web...
 

Offline Boudicca

Re: Any Raid Experts?
« Reply #5 on: June 24, 2010, 08:21:10 AM »
Quote from: trekiej;566867
I am planning to build a new computer and I wanted to get some advice on Raid5 and Raid 1+0.


* All but a few so called "Cheaper" NAS Raid devices have any decent transfer rates. i.e Gigabit networking doesn't necessarily mean Gigabit Transfer speeds, and most aren't anywhere close to a PC with the same.

* "Fake" Raid is common on many cheaper raid controllers and many built-in mainboard raid controllers. The upshot is that its just in enhanced software raid and many OS's don't support it well.

* I can recommend Adaptec SATA Raid controllers specially the 4, 6, or more port cards as they are hardware raid. (Sadly however Adaptec have been bought out so support will diminish.)

* Depending on the resilience you want Raid 1 and Raid 1+0 is the by far the most resilient, Raid 5 is much weaker, unless you use a hot spare.
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Offline Colani1200

Re: Any Raid Experts?
« Reply #6 on: June 24, 2010, 09:24:08 AM »
Quote from: trekiej;566867
I wanted to get some advice on Raid5 and Raid 1+0.

RAID5: You will need at least 3 disks. Net. capacity will be 2 disks then.
RAID1+0: You will need at least 4 disks. Net. capacity will also be 2 disks then. Will be faster than RAID5

In general I would advise to buy a fast SSD nowadays instead of filling up your computer with a pile of power consuming, noisy, heat generating conventional drives. At least if we a talking about a desktop. If you need a lot of space, think about a NAS solution as others mentioned before.
 

Offline Piru

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Re: Any Raid Experts?
« Reply #7 on: June 24, 2010, 09:31:20 AM »
Quote from: Colani1200;566912
RAID5: You will need at least 3 disks. Net. capacity will be 2 disks then.
RAID1+0: You will need at least 4 disks. Net. capacity will also be 2 disks then. Will be faster than RAID5

Small clarification: Faster than RAID5 when writing. Reading is pretty much the same.
 

Offline d0pefish

Re: Any Raid Experts?
« Reply #8 on: June 24, 2010, 10:19:47 AM »
I use a RAID5 setup with 4x WD Caviar Blacks on a dedicated RAID card (Areca 1222 PCIe).

This array of 4x1TBs gives an effective capacity of 3TB, and transfer speeds are extremely fast as the controller accelerates RAID5 operations in hardware with none of the overheads in processing incurred by using a software RAID solution (as commonly found using on-board motherboard controllers for RAID). It also has a 128MB cache on board.

The Areca is a joy to work with, it's an expensive card but very robust and intuitive to set up.
You can split the array up how you like so they appear to the machine and OS as more than one "drive" if you like. For example, my 3TB array is split into two "drives", one 120GB for operating systems, and the rest as storage for programs and data. This is useful for situations where the array size is too big for an MBR partition scheme, or where setting up a multi-boot environment with lots of extended MBR partitions could be a headache to get working.

The card has a web interface accessible via the driver to configure and monitor it, and also has an Ethernet port so it can be accessed from another terminal on the network, but also broadcast warnings and other information to wherever an administrator may be monitoring.

I chose the Areca for its excellent driver support; it has drivers for all flavours of Windows, both 32 and 64bit. Linux support is in the kernel, and MacOS X has support for it built-in for use in a hackintosh application (;)) or for use in a Mac Pro.

It is a server-class card with tons of features, and probably excessive for a home machine, but I can recommend it.
 

Offline pyrre

Re: Any Raid Experts?
« Reply #9 on: June 24, 2010, 12:28:30 PM »
Quote from: trekiej;566867
I am planning to build a new computer and I wanted to get some advice on Raid5 and Raid 1+0.

Depending on your use of the computers storage.

RAID 0 Stripes multiple disks together, and such increasing capacity.
This is (in theory) the fastest raid setup.
No real limit to size. Apart from what your OS can address(close to 12TB on 32bit OS)
But there is absolutely NO SAFETY or fault tolerance. one disk dies, your entire raid dies, and the data stored on it as well.
(and believe me, restoring such data is EXPENSIVE)

RAID 1 Mirrors minimum two disk.
Write speed is quite slow. Read speeds are average.
Fault tolerance is one disk may die and data is still intact.
If more than two disks are mirrored, fault tolerance increases.
But capacity is limited to only one disk.

RAID 0+1 are combinations of striping and mirroring. Increased speeds and capacity.
And maintaining some degree of fault tolerance.
This setup is mostly limited to 4 disks. (more than 4 disks makes it VERY uneconomical)

RAID 5 same as RAID 0, but with certain advantages.
It needs at least 3 disks and it uses one disk for parity. Fault tolerance is one disk.
However if you are planing on running it with more than 10 disks consider RAID 6 instead.

RAID 6 same as RAID 5 but with two parity disks instead of only one.
Useless on raids with few disks. but becomes mandatory on large raids.
It will withstand a fault of two disks failing simultaneously.
Great when running a raid of 16 disks.

---------------------------------------------------

After doing some testing. (on PATA and SATA disks)
Raid 0 and 5 increases speeds significantly until four or five disks are reached. But are sometimes maxed out at two or tree disks.
RAID 0 is by far the fastest raid configuration. (but it has NO fault tolerance)

Speed is limited by:
Average seek time, disk cache, internal transfer speeds, bus speeds, controller cache, internal controller speeds....

By raiding two 220MB/sec SSD disks read speeds of 400 MB/sec can be achieved.
But don't expect miracles from ordinary disks. 150 - 200 MB/sec can be achieved...

----------------------------------------------------

To cut things short.
If you need speed and don't care about fault tolerances. RAID 0 is your thing.

If safety comes first, RAID 5 is recommended.

If you like me are completely paranoid by disk failure. Then RAID 6 is mandatory.
---------------------------------------------------
As for RAID 0/1/0+1 (mirroring). i don't see no real use...
Striping two disks and then mirroring them with two more disks... it just wastes one disk and it will only tolerate one disk failure. (unless both disks of the mirror or stripe fails at the same time.)

By using RAID 6 and the same four disks.
still only two of them will represent the available storage. But it will withstand a two disk failure. maximum safety.

-------------------------------------------------------

EDIT: Adding a link to wikipedia article about RAID: http://en.wikipedia.org/wiki/RAID
EDIT: Correcting some facts.
« Last Edit: June 24, 2010, 12:45:10 PM by pyrre »
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Offline Iggy

Re: Any Raid Experts?
« Reply #10 on: June 24, 2010, 03:57:44 PM »
I've had a lot of luck with Raid 1 and Raid 0+1. In every instance where I've had a drive corruption, I've been able to recover from the good drive.
I'd highly recommend these two methods.

The risky Raid setup is Raid 0. Your actually doubling the change of losing your drive info.  Should either drive fail, you're done.
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Offline johnklos

Re: Any Raid Experts?
« Reply #11 on: June 24, 2010, 09:42:25 PM »
The best bang for the buck for multiple drives is to get a HighPoint eSATA RAID card. The 622 is a two eSATA port card that can use up to 10 drives, and the 644 or 2314 has four ports and can use up to 20. eSATA port multiplier enclosures are not horribly expensive. A Sans Digital five bay enclosure, for instance, is around $200 USD from NewEgg.

RAID-0 (sic) shouldn't even be discussed. It's not RAID since R in RAID stands for redundant, and striping drives makes things less safe than keeping them on a single drive. (Is there such a thing as negative redundancy?)

The simplest RAID setup is simple mirroring. Most x86 motherboards support BIOS-based mirroring. I'm not sure whether Windows has software mirroring, but just about any Unix-like OS (BSD, OS X, GNU/Linux) has software-based mirroring. You can also buy hardware-based mirroring enclosures which appear as one drive to OSes which don't have support (such as AmigaDOS).

If you're worried about viruses, then that implies you're using Windows. There's nothing RAID can do that can save you from that. Your only option then is to maintain two copies of everything, which is what others have said above.
 

Offline Boudicca

Re: Any Raid Experts?
« Reply #12 on: June 24, 2010, 09:51:08 PM »
Check this list out, its a bit out of date but useful, avoid anything that says "fake raid", i.e its hardware tied software raid.

http://linuxmafia.com/faq/Hardware/sata.html
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Offline alexh

Re: Any Raid Experts?
« Reply #13 on: June 24, 2010, 10:33:24 PM »
Quote from: Piru;566913
Small clarification: (RAID 1+0) Faster than RAID5 when writing. Reading is pretty much the same.
Reading will be much faster than RAID5 with more than one application accessing different areas of the drive. The OS or RAID card will monitor the last LBA of each pair and target the closest pair. This greatly reduces seek time.
« Last Edit: June 24, 2010, 10:35:35 PM by alexh »
 

Offline trekiej

Re: Any Raid Experts?
« Reply #14 on: June 24, 2010, 11:46:28 PM »
Thanks.
An Article I was reading said that the user should have Backup Storage in case of a raid failure.
It also said ( or another post ) that cost wise that Raid 1+0 was better than Raid5 on the second disk failure.
For a newbie, it looks like the Holy Grail, when it fails it becomes a Holy Cow. :)
The board I want to get has 6Gbs SATA. How can I push that to the limit?  
Do I need SSD's or many HD's?
Can a raid system beat the bloat? :)
« Last Edit: June 24, 2010, 11:48:49 PM by trekiej »
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