How Does Windows Manage Raid 0?

[Snacko]

I bought a laptop with 2 500gig drives in it. It said it came with RAID 0 already setup. I have never used Raid before, but know enough to be dangerous. From what I read, Raid 0 Treats the two drives as 1 larger drive.

So, does it all start with the BIOS seeing them as just 1 terabyte drive?

When I look in Windows I see it partitioned with 2 hidden partitions, and two visible partitions: C: (530gig) named as 'OS_Install' and D: (325gig) named as 'Data'. So, all four of these partitions are seen as part of the one Raid 0 drive?

I am a little confused because in Windows I still see a C: and D: drive. And I do have two physical 500gig drives.... I am guessing them just made two partitions so you could have a place to back stuff up? Not sure

But in the Disk Management I see one physical Disk 0. With C: And D: and the other two hidden drives on that one Disk 0. So, Windows must treat these two disks as one disk and then partition all of the partitions in that one disk..

If I have that correct so far, I am wondering how Windows takes advantage of this to make the system run faster?? Does it take every file in the system and put half on one physical disk and the other on the other physical disk so that it actually has two devices spinning and two read/write heads, thus doubling the access speed? ??

Why do they name the C: drive OS_Install, and the D: drive Data? If as I guess, every file is split on each physical drive for speed, then separating the OS from Data/Programs/etc. would not be necessary??

So, should I ignore these drive 'names'? and just use the C: for installing all programs and D: for personal data like My Documents; Pictures; Movies; stuff I want to save..

Sorry this confused though stream here.. but I have to run out the door and wanted to post my confused thoughts about this before I left. So, maybe I'll have an answer when I get back... I am at the point where I am read to start installing games, and many of my programs and am wondering if there is a point to installing them to the D: drive at all... Plus I want to make a backup image before I do all that as well...

Snacko

[B16Enk]

Hard to say, without looking in BIOS, but sounds like this is a JBOD or a single dsk from BIOS level.

Presented to Windows as a single device, and then partitioned.

So files are spread across both disks, not 'split' so no performance gain.

[Snacko]

I also received an email from this post that said Pooka had posted this video. I don't know why his post doesn't show. But thanks Pook..

http://www.youtube.com/user/NCIXcom#p/u/62/RYBtmVMtH1g

So, he explains that every other bit is written to each drive. While I thought that each file was split over each drive, I can't imagine that every single alternating bit goes to alternating drives. Instead of reading bytes or words of data, wouldn't it have to do a read/write operation for very single bit? Maybe the raid process breaks them apart and writes them each as bytes or words, and reads them that way as well and then raid puts the files back together? Something like that must be happening.. But I digress..

And here is a link to my Laptop.

http://www.newegg.com/Product/Product.aspx?Item=N82E16834152266

It is definitly 2x 500gig drives using Raid 0. The sticker on the laptop as well as everything else says this.. I have not look through the bios yet, but will do that shortly. But on boot some screen flashes by about pressing Ctrl-I to configure the hard drives.. Haven't had a chance to look at that either..

So, assuming it is 2 drives at Raid 0, there does not seem any good reason to install any programs on the D: drive for performance, right? In essence, that is already happening with everything..

Now I need to find out how Acronis TI Home 2011 will handle drive imaging.. I just want to image drive C:... I read it will work, but since raid 0 writes to both drives, and Acronis does not like to backup on a drive it is imaging... I may not be able to just backup to my D: drive.

[DD_Brando]

I think that you need to back up your Raid0 to a separate HD altogether, and I think that Acronis will enable that. Raid0 is faster than one single disk because of the data being split and distributed across two drives - or striped - but it is vulnerable to total loss if one of the drives breaks down. Whereas Raid1, where the data is mirrored onto both hard drives, is safer than a single disk because, if one drive dies, all the data is still on the other. Raid1 does not have a speed advantage though.

Its best to think of a striped array -Raid0 - as one single hard-drive for working purposes. I believe the Raid array can still be partitioned like any drive, but the partitions are still spread (striped) across the two disks in the array. Therefore, backing up on the Raid0 is still vulnerable to the physical loss of one HDD.

Now, it is possible that some clever software exists that allows part of a Raid(ed) disk to be formatted in the standard way, so that the data is all there rather than striped, but I haven't heard of it. Mind you, when I was Raid0'ing drives to get a little extra oomph I was using 40Gig Maxtors! So some tweaks may have been worked out since.

The best way to see this is as follows: 1) Your two hard-drives (500Gb each) are in Raid0, a striped array. Consider it as one large space, nearly 1 Terabyte, which will be shown in Windows as your default C:\ drive. Whoever programmed it may have partitioned the space to separate the operating system (Windows & apps) from simple data storage (films, pictures, music and so on) This second partition will likely default to D:\ - just the same as if you only had one hard drive.

2) Note though, this data (D:\) is also striped across two disks and therefore dependant on Raid0 to access it......

3) Which is why you could back up the data to a single, separate hard drive large enough to accommodate it (i.e a 1 Tb drive).

[Snacko]

Thanks Brando, that helped a lot...

I did just finish using Acronis TI to image my Disk 0... It was only a 70gig backup image and included all 4 partitions (C:, D:, and 2 hidden recovery partitions). So, for a worst case scenario I think I am covered.

I agree that they then partitioned the raid 0 into C: and D: for OS and personal data. This does make it easy to backup personal files and image the OS for restore to earlier/cleaner versions.

I plugged in my eSata External 1T LaCie Backup Disk and stored the backup images on that drive, so if I have a drive failure, I can boot from an Acronis Recovery disk and use the eSata Drive for restore.

Thx for the replies.

Snack

[B16Enk]

Unusual for native MOBO BIOS to support true raid other than mirroring.

Generally they offer only JBOD and RAID 1, the former being 'Just a Bunch Of Disks' with no parity or striping, the latter being as we know redundancy with parity and no performance gain.

Taking the time to look up your chipset spec however I can see it does offer RAID 0, as well as 'Matrix' and Intel spec where it will nest/combine RAID 0 and RAID 1.:

Performance with Protection: Matrix RAID

For those users who wish to combine the benefits of two RAID levels, matrix RAID is the solution. When using two hard drives, matrix RAID allows RAID 0 and RAID 1 functions to be combined, where critical files can be stored on RAID 1, and RAID 0 can be used for non-critical items such as software. In 2005, the matrix RAID capability was expanded to include RAID 5 and RAID 10. For instance, RAID 5 and RAID 0 can be combined to provide higher performance, capacity, and fault tolerance. A user can edit digital video on a high-performance 4-drive RAID 0 array, then transfer it to RAID 5 for protected storage when completed.

Looks like pressing CTRL + I to see what it is setup as

Utilities such as Acronis will see the drive(s) at the logical level rather than the physical, so no change in behaviour.

[Snacko]

That's interesting. I did look at the bios and it does not have much at all compared to my Asus Rampage II Extreme. It only has 4 main screens. Pressing Ctrl-I does bring up the Intel Raid screen. I looked around, but I'm not messing with that.