Question about Windows-level RAID/spanning/etc

[vetteguy]

I did some work on my server over the weekend, and decided to implement some Windows-level RAID with my drives. I have 2x160GB which I am mirroring, and 2x250GB which I wanted to combine into one large drive. I currently have them set up to be striped (the data to be stored on there is not anything I can't afford to lose, plus I have backups) but when I was doing it I noticed you can also span a volume to encompass multiple drives. Since I'm not overly concerned about the speed on this array, I was wondering if spanning might make more sense, but I had a question-I know with the stripe, if one drive takes a dive I lose everything. What about in a span? If I lose one drive, will the data that's physically stored on the other drive still be accessible? What about if I lose my Windows installation? Like I said, I'm not too concerned with safety of this data, but if spanning gets me the same benefits with less risk than striping I might just do that.

 

[airfoil]

Unless you implement RAID5 (Disk striping with parity, which requires 3 drives for striping + one drive for parity data), yes, you'd lose data in any other arrangement which invloves spanning.

 

[vetteguy]

Originally posted by: airfoil
Unless you implement RAID5 (Disk striping with parity, which requires 3 drives for striping + one drive for parity data), yes, you'd lose data in any other arrangement which invloves spanning.

I know, but my question was, if I just did a normal span (not striping), and if one drive failed, would I lose ALL the data on the spanned volume, or would the data that physically resides on the "good" disk still be accessible? I've done RAID before, but I've always used hardware controllers, this is the first time I've played with software RAID.

 

[sharkeeper]

It sounds like you're confusing striping (RAID0) with JBOD. If one disk fails with striping, it is nearly impossible to get your data back. If a disk fails with JBOD, you should be able to easily recover what's on the good disk.

Cheers!

 

[vetteguy]

Originally posted by: sharkeeper
It sounds like you're confusing striping (RAID0) with JBOD. If one disk fails with striping, it is nearly impossible to get your data back. If a disk fails with JBOD, you should be able to easily recover what's on the good disk.

Cheers!

That's what I was asking...as I said, right now I've got it striped. The other option was volume spanning, which I guess is the Windows vernacular equivalent of JBOD. I've never played with JBOD on a hardware controller before, so I didn't know how it handled single disk failure. That's what I needed to know, thanks!

 

[VirtualLarry]

Originally posted by: sharkeeper
It sounds like you're confusing striping (RAID0) with JBOD. If one disk fails with striping, it is nearly impossible to get your data back. If a disk fails with JBOD, you should be able to easily recover what's on the good disk.

Cheers!

I think that it kind of "depends". I don't think that either option is really that safe. Consider both the FAT32 and NTFS filesystem. FAT32 stores the file-allocation tables at the beginning of the drive layout, and files tend to get fragmented fairly easily. If the first drive out of the JBOD set goes, the one containing the FAT tables, it will be very difficult to sucessfully recover the rest of your files from the other drive(s), especially in the (likely) event that they are fragmented. Now let's look at NTFS. From what little I know about the actual physical layout of that filesystem, it tends to attempt to place the critical MFT table in the center of the drive, in order to optimize seeking between it and the files on the volume. That means, that with a two-drive JBOD set, if either one of them fails, then they will take half of the MFT with it, leaving precious little to use to recover the files on the remaining drive. If one used a three-drive JBOD set, and lost the middle drive, the entire MFT would most likely be lost.

So in all cases, you are very likely to lose everything, should one drive in a JBOD set go. The only case in which this wouldn't happen, is with FAT32, and losing a drive other than the first in the set.

If you wish to use multiple disks, and not stripe nor span, then consider simply setting up an independent filesystem on each drive, formatted NTFS, and then use the NTFS "directory/partition mount feature", to mount the drives as a subdirectory of some primary mount-point drive (OS boot/system drive, most likely). This is such a fundementally-basic feature in *nix, but most NT users don't know about it or use it very much. That way, each drive has its own indepedent filesystem, and if one drive fails, it only takes out that filesystem, not anything else.

 

[vetteguy]

Originally posted by: VirtualLarry

Originally posted by: sharkeeper

If you wish to use multiple disks, and not stripe nor span, then consider simply setting up an independent filesystem on each drive, formatted NTFS, and then use the NTFS "directory/partition mount feature", to mount the drives as a subdirectory of some primary mount-point drive (OS boot/system drive, most likely). This is such a fundementally-basic feature in *nix, but most NT users don't know about it or use it very much. That way, each drive has its own indepedent filesystem, and if one drive fails, it only takes out that filesystem, not anything else.

This is the way I have done it in the past, the problem is it makes it inconvenient to use all of your drive space from a single share. I had 2x160GB both formatted separately, with one shared off its root, and the other as a mounted volume in a folder in drive #1. The problem was, I wanted to access all 320GB from one sharepoint on all of my PCs, but instead I was able to see 160GB, and then I could drill down to the mounted folder and get the other 160. This was a hassle because 1. I had to split stuff up more than I wanted to, and 2. it was a chore to see how much free disk space I had at any given time. Like I said, I'm not overly concerned with the safety of the data, as this will mosty be mp3s, movies, etc, things which are backed once and then don't really need to be backed up again.