Monday, 25 July 2011

Test runs

Did a RAID 6 test on an Intel SRCSASBB8I controller (LSI 1078 chipset, also used in Dell PERC 6/i), and it was successful save for a couple minor issues. First we got the R-Studio RAID matrix rendered wrong (data blocks are off by one), and also under the hood it looks like the analysis can use some more noise reduction. Still, the output image is OK. This applies to ReclaiMe Free RAID Recovery build 397 at www.freeraidrecovery.com.

Wednesday, 20 July 2011

RAID 1E analysis delayed

If you want some unusual RAID layouts, call Promise. So far, Promise controller has the most bizzare RAID 6 variation we've seen, and also gave us a nasty surprise with RAID 1E.

Typically, RAID 1E would be laid out as follows

1 1 2
2 3 3
4 4 5
5 6 6

(the above is so-called NEAR layout)

or
1 2 3
4 5 6
7 8 9
3 1 2
6 4 5
9 7 8

(the above is FAR layout).

Now Promise combines the best of both worlds to produce a third variation (Promise 1E layout)

1 2 3
3 1 2
4 5 6
6 4 5

Looks promising, doesn't it?

So, the implementation of RAID 1E recovery capability in ReclaiMe Free RAID Recovery (www.FreeRaidRecovery.com) is delayed until we figure out how to handle this one.

Thursday, 14 July 2011

Detecting RAID0 where it is supposed to be RAID5

Recently, a question arose about our RAID recovery software (www.freeraidrecovery.com), along the lines of "There is a RAID5 array, but I get some results if I try to recover RAID0 as well, what's wrong?"

Actually, there is nothing wrong. RAID Recovery requires the array type as outside input, along with the list of member disks. It has no way of determining if the provided array type is correct or not. Therefore, it tries to produce the closest possible layout for a given array type. There are certain cases (mostly involving RAID6) were nothing meaningful can be constructed, and it gives up with the appropriate error message. However, in most cases some layout will be produced.

If the original array type is not readily known and it is not possible to infer it from the number of disks and available capacity, the only solution is trial-and-error testing of all possible layouts (of which there are about four fundamentally different, RAID5/5E being practically equal).

Thursday, 7 July 2011

Mapping device identifiers to drive letters in Windows.

If you get an error message similar to The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume \Device\HarddiskVolume1. there may be trouble matching the identifier \Device\HarddiskVolume1 to a drive letter (is it C:?) or an actual physical device.

Most of the time, finding the corresponding drive letter (X:) is good enough because you can then look it up in the Disk Management console.

However, the trouble is that \Device\HarddiskVolume1 is not referenced outside the system event log.

To find out the list of mappings, download and run the Microsoft Product Support Reports utility from http://www.microsoft.com/download/en/details.aspx?DisplayLang=en&id=24745

When it asks you what to collect, you only need the most basic option, something like "Basic information" or "General information". When done, choose to "Open and view the result" - Windows Explorer will launch and open a folder with a file "Master Report.xml" and subfolder "General".

Go down to "General" folder and find the file "ComputerName-DOSDevices.TXT". Open it and you get your mapping list at the very top of the file.