Altirium Data Recovery Blog

Archive for the ‘Data Recovery’ Category

I’ve often heard it said, “the RAID has been rebuilt – the data cannot be recovered” and often this is the case. With RAID5, if the configuration is changed, and new parity is calculated, then there will be a significant loss of any data that was previously stored on the RAID.

As Hamlet so eloquently put it “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”, just because something is outside of our normal experience does not mean that it is not possible.
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Tivoli Storage Manager (“TSM”) provides a sophisticated heterogeneous data storage environment within which large volumes of data can be held. These might include email backups, user documents and SQL database, in fact all of the information that might be just a little bit useful in a computer forensic investigation or a tape data discovery exercise.

So, you are an investigator who has been handed a case containing 25 LTO4 cartridges from a TSM archive, now what?
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When attempting a data recovery from a Microsoft Exchange email server after a catastrophic failure, and when I say catastrophic I mean, no backup to restore from and file system corruption or file deletion that has rendered the Exchange information store files inaccessible, one of the tools in Altirium’s data recovery arsenal was to trawl the entire disk or RAID volume and identify pages of Exchange data and rebuild the information store from the ashes. However when Microsoft engineers decided to change their page error correction method so that they could correct a single bit error in a page this seemingly minor ‘upgrade’ had dramatic effect in the ability to identify Exchange page data.

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The popularity of Network Attached Storage (NAS) RAID units has never been higher. For a small outlay a low powered, easy maintenance, storage device of 1TB or higher can be plugged in and used where once an expensive server with disk storage would have been the only option. Whilst RAID5 gives a high degree of reliance against the failure of any one disk in the NAS unit, other problems can result in an apparent total loss of data and a requirement for a NAS Data Recovery.

A NAS storage device  in need of recovery was delivered to us last week. The customer had been using the device and on Friday evening all data was present and correct, but when the customer went to access the device on the Monday morning it was operational but there was no data present. So where had it gone and could a data recovery be achieved?

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TK50 was a major player in tape backup on VAX/VMS systems several years ago. Being fundamentally ½” (half inch) tape of the type used in open reel drives, but housed as DLT style cartridge, it suffers from the same long term storage problems as some brands of 1/2″ media. TK50 drives could store 70MB of data, and took quite a long time to fill, so have long since ceased to be a viable backup option even if you can find drives and media. But, there are a surprising number of tapes out there with data on them and recent weeks seem to have brought forth a flurry of requests to get data from them, and in one case to copy some. In a high proportion of these cases the data transfer operation has ended up being a data recovery exercise involving considerable work in the lab.

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When I first started in the data recovery industry back in 1995 data recovery was very much a specialist area of expertise. There were no ‘off the shelf’ data recovery software tools. We had to develop our own methods and techniques to get the job done. These days however the data recovery market place is flooded with companies offering such services, so how do you know who to choose?

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Much data recovery work involves the salvage of data from one specific type of storage, a hard drive, RAID array, backup tape or DVD. Occasionally a requirement pops up that transcends this norm.

Having faithfully adhered to a regime of nightly backup of a SUN UNIX system, the failure of the hard drive appeared to be an inconvenience that would soon be overcome for this customer. The hard drive having swiftly been replaced, the backup tape was brought back from storage and the restore process initiated. Five minutes in, however, and the DLT drive made a nasty noise, the cleaning lights came on and ufsrestore became ufs-cannot-restore.

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RAID 5 combines capacity and performance with fault-tolerance, a disk can fail and the RAID will keep on going, so does this mean that there is no need for backup? Is RAID 5 data recovery never going to be a requirement?

Some people seem to think so, but have been dangerously mis-informed. The error correction used in a RAID5 array is there to provide a level of protection for what will often be business critical data, but can still only survive the loss of a single hard drive from the array. Even RAID 6 with double error correction can only cope with a failure of two drives.

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“How many layers of data can you go down on a hard disk drive?” was the question over the phone. Not really a silly question, there is so much mis-information about how hard it is to erase data from hard drives, and how “data-can-be-recovered-even-after-the-platters-have-melted” (possibly the latter is a slight exaggeration).

It is worth debunking the myth quickly. With a hard disk there is a single layer of recordable material on each side of each platter. When an area of this disk is written to, whatever was at the area previously has gone forever. No need to write over it seven times, no need to sandblast the disk.

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The recovery of data files that have been deleted is not always a matter of competence, to a great extent success is governed by the file system in use and how busy the system has been since the deletion.

Windows NTFS, for example, marks a file as deleted but until the MFT entry is reused all of the file’s allocation information is still present. Other systems clear some or all of a file’s allocation information as soon as there is deletion, which is why the recovery of deleted files from heavily fragmented FAT file systems is such a nightmare.

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