A quick question about RAID

vbimport

#1

Hi :slight_smile:

I’m here with another crazy question :doh:

Most (if not all) mainboard have RAID controllers embedded in the PCB, but I never used a RAID system.

After the HDD crash, however, I’m considering to use it to build a RAID1 configuration.

Is it possible to build more than a single RAID array (I hope that “array” is the correct term)?

For example, if the mainboard has 4 SATA slots, is it possible to use 2 of them to build a RAID1 with two HDDs, and the other two slots to build another RAID1 completely separated from the other? In this way it should be possible to have two separate storage buckets.

I’m not even sure if this makes sense. I’m just curious :bigsmile:

BTW, is it better to not use the embedded controllers and get a PCI/PCIe card instead?

Thanks :bigsmile:


#2

Technically it’s all possible. It all depends on the controllers. Embedded controllers tend to have less possibilities than specialised RAID controllers.

RAID volumes are built using harddisk volumes. If you define a 200MB volume on both harddisks, you can make a 200MB Raid 1 volume. Of course it is no use to RAID 1 two volumes that are on the same harddisk.


#3

Thanks for the answer :slight_smile:

I’m scanning stores to find reasonably priced disks :bigsmile:


#4

I’m not sure if you can do this on “onboard” RAID with for example, Intel ICH but the following setup would be ideal.

Create a small RAID 0 volume for the OS with the two fastest drives of about 80GB if it’s XP or Win7. That way you have speed for the system (RAID 1 is slow as an OS drive).
With the remainder of the space on the two fastest drives, create your first RAID 1 array.
Add your other two drives as a separate RAID 1 volume

With the above setup, you’ll have speed and safety.

In all cases, you will need to do a fresh install of Windows to get it working anyway. Win7 is the easiest, if your using XP, you’ll need to make a RAID driver floppy so you can install XP. Win7 already has RAID support out of the box.


#5

My plan was to get a SSD for the operative system and programs only, so I could use HDDs for storage only, but of course the wallet is not agreeing :doh:

The reason why I asked about the multiple array is that in this way I can create two separate storage buckets. I found at a reasonable price samsung F3 1TB drives, so if I get 4 of these drives I can have two separate 1 TB data storage sets.

Any suggestions about a reasonably priced PCI/PCIe controller to do this? :slight_smile:


#6

It should be mentioned that Intel Matrix RAID isn’t near real hardware RAID and I’ve seen several reports of ppl not being able to recover probably using Intel Matrix RAID (ICH-based RAID).
//Danne


#7

[QUOTE=DiiZzY;2532139]It should be mentioned that Intel Matrix RAID isn’t near real hardware RAID and I’ve seen several reports of ppl not being able to recover probably using Intel Matrix RAID (ICH-based RAID).
//Danne[/QUOTE]I have heard that as well, and software RAID (Intel Matrix) is no substitute for real hardware RAID.
Unfortunately, real hardware RAID cards will set you back 200 euro or more. Also using RAID makes things more complicated, and the more complex something is, the more likely you are to have problems.

4 drives also means there are now four drives that could fail rather than single drive. If it were me, and i needed 2TB of storage space, and wanted a safe system. I’d buy 2x 2TB drives, use one for storage, and backup that storage drive to the other 2TB drive. It’s really only a matter of dragging and dropping new files across to the backup drive. That’s my solution and its problem free, so far. :slight_smile:


#8

That would be RAID 1 (mirror), RAID 6 can handle two drive failures and RAID 5 one.
ZFS and RAID-Z (similar) have been working fine for me for at least a year now and that’s software raid gone good. :slight_smile:
//Danne


#9

I found some information on Wikipedia… it seems not really a simple thing :o


#10

So many RAID levels, and mixes.

Intel matrix RAID, for instance, is pretty versatile in the kind of volumes it can handle and build usi9ng whole drives or parts of drives.

Just as with hardware versus software modems, it seems there are the same distinctions:

“Hardware RAID” would have the parity calculations in hardware.
“Software RAID” would do it all in software.
Motherboard RAID tends to be inbetween, if using for RAID 5, it would be calling on the host CPU for the parity calculations.

Now RAID 0 and 1 do not use parity, RAID 0 is disk striping, RAID 1 is mirroring, and the levels can be combined - with 4 drives:
Raid 0+1 (mirror of stripes), or RAID 1+0 (stripe of mirrors).

Pretty sure most will also allow you to make two seperate arrays - one use being to make a fast RAID 0 stripe for OS and apps, with a RAID 1 mirror set for data.

The onboard controllers tend to have a bus efficiency advantage due to their closer coupling with the chipset, so will often be better than anything that isn’t a “smart” (and expensive!) add-on card.


#11

If you want to use RAID (for some kind of insurance/reliability) you’re better off running it on a file server of some kind (NAS/SAN).
//Danne


#12

Personally I wouldn’t use RAID for mirroring disks on a personal computer - I don’t believe the complexity is worth it, and mirroring ONLY protects you from harddrive failure - it doesn’t protect you from other things such as user error or virus infections.

Instead, if you want to minimize the impact of harddrive failure, I would use mirroring/cloning/backup software, and keep the extra harddrive unmounted most of the time.

If you run a server for multiple users, then RAID makes more sense in my opinion.


#13

You could get a 3Ware 9500S-4 on eBay for about £50 - that is a true hardware RAID card and has 4 SATA ports. It supports RAID 0,1,5 & 10.

I have a 9550SX-12 in my server and a spare 9500S-4 as a backup (both RAID5 arrays in the server have 4 members).

I have found 3Ware cards to be very reliable (I have had 5 in total - all from eBay) and haven’t lost any data in 3 years.


#14

Thanks everybody for your answers :slight_smile:

I think that I’ll get a couple of HDDs to be used in external boxes or SATA --> USB adapters. It is certainly the best option for me :bigsmile:

Maybe in future I’ll try to build a very simple NAS with an Atom board and a spare case, but for now the wallet said to get the HDDs only :doh:


#15

No real point getting a “real” RAID-card for [B]home users[/B] now that ZFS is available.
It’s still not a substitute for having a backup.
//Danne


#16

Gents,

I’ve done RAIDS on quite of few Boxes using Motherboard based controllers (almost always Asus MBs). Early on using two IDE (80 Gig) drives for Speed (striped) for just the OS and core programs. It solved the bottleneck at the drives. Later after a large SATA drive failed on a Buddy’s Box with all his photos, movies, tunes, etc., he begged me to build his next box with a mirrored array to protect his data. The 3rd Box I built him (i7 920 CPU with 12 Gigs of DDR3 about 11 months ago) had 4 one TB Drives in a striped and mirrored configuration. (Both Quick and Redundant. The OS is on a small partition and Data on another.)

He wants the next one to have striped SSDs and mirrored 2 TB Data Drives.

Personally, I dropped Raid configurations and went to Ghosts of the Operating Partition (one on a Data Partition and another off the machine) and separate hot swappable Data (and / or another OS) Hard Drives. I use 2 SATA Internal Hot Swap Racks in my main Box. I keep 3 hard drives just for data archives, and another 5 or 6 with various combinations of data and Operationg systems.

I dream about using 2 SSDs in a Striped array for the OS but the cost is still a bit prohibitive. :flower:


#17

Jim et all,
Raiding just 2 SSD’s will see little gain.
To get the best out of Raid, separate controller is almost a necessity.
I had used raid almost constantly for 12 years.
From true SCSI to s/w emulation.
For most home users raiding SSD’s is all but pointless.
Have OS on 1 SSD (save an image to external source).
I use the smallest/frastest SSD for my OS ( + what I feel to be essential s/w).
The rest, like media library go onto HDD’s (non- raid).
Using external HDD dock (backups, imaging etc done the same way).
Media conversion/compression etc done by 8 HDD’s Raid0 using additional raid controller (so not s/w emulation).

N.B.
Using 2 SSD’s Raid0 will only give about 1 > 2 % improvement for most users via s/w raiding.
So a minimum of 3 ( but more would be better) if Raid0.

Raid1 save money have 1 SSD & mirror by cloning drive to a HDD for backup purposes.

Possible useful link: - http://www.acnc.com/04_00.html


#18

Soulsurvivor,

I agree RAIDs really are not needed for most folks, but for those who are too lazy (or are not competent) to back up the data on their machines (and have extra $ to spend on hardware) they fit the bill.

For the OS/Program side I disagree on the RAID not being beneficial using SSDs. My reading indicates SSDs when striped almost double their reading performance versus marginal improvements in writing, and that’s really all the OS/Program drive does - read (once installed).

If you can reference counter information please share the link before I spend $ for 2 drives (some day). Thanks for the assist.


#19

SSDs in RAID0 scale well regarding sequential reads and writes, 4K random write speeds also scale well. 4k read doesn’t scale at all in RAID 0, plus latency increases.

For audio, video editing, RAID 0 SSDs are awesome, for most other user patterns, a single SSD is as fast as two in RAID 0, and many many times faster than any HDD.


#20

I just ordered a couple of 1 TB HDDs, to replace the damaged one, and I’ll do a “manual” 1:1 mirroring (i.e. I’ll copy every file in both discs by myself :bigsmile:)

At the moment this is the only solution I can afford :doh:

But building a NAS (sooner or later) is still in my plans :iagree: