Friday, 20 August 2010

RAID5 diagram fail

(Taken from WD site)

What's wrong with the picture?

Select the whitespace below for an answer
In the above RAID5 picture, there are two parities in the middle row. In a proper RAID5 there must be exactly one parity per row.

Monday, 16 August 2010

Upcoming: free RAID recovery software

We are now developing a RAID recovery software. As you know, RAID recovery boils down to two independent steps - RAID parameters recovery and the subsequent recovery of data off the reconstructed array. Knowing the array parameters, the data recovery (second step) can be done using any data recovery software. The RAID parameters reconstruction is not such an easy task, and frankly speaking, there are very few RAID reconstruction tools.

So, we decided to develop our own RAID parameters recovery software, which we think would be the best of ever been, and at the best possible price.

Our RAID parameters recovery software will work with RAID 0 and RAID 5 The output would be either a parameter set, or an image file of the entire RAID array. The option to write the array data directly to the specified device is also considered.

We are planning to release the software by the end of September (year 2010, you know). All the other specifics like download location is still to be determined. Keep an eye on our blog posts.

Saturday, 7 August 2010

Partitioning in modern systems

In the early days of computing, partitioning disk to several volumes was sometimes a good idea. Now, “one disk – one volume” is the most practical way to go.

The original factors and reasoning behind having multiple partitions have much less significance now. The maximum available volume size, limited in FAT16 filesystem, is no longer a factor. Modern filesystems such as NTFS have much smaller clusters for a given volume size, so the loss of space to slack is much less a concern.

There are few exceptions,

  • When an extremely large RAID is involved, a single volume may be impractical because of the backup and the filesystem consistency checking considerations. Last but not least, the read-only data recovery requires a lot of free space same size as the damaged volume; this may be difficult to provide for a gigantic monolithic volume.
  • If multiple operating systems are required with multiple different filesystems, then having several partitions is perfectly justified.

The most common side effects of having multiple partitions are:

  • Free space gets “fragmented” – although the combined free space may be large, the individual partitions would not have enough free space to hold whatever monolithic disk space block is required.
  • If the data is somehow logically grouped (e.g. “OS” and “data” partitions), disk space requirements are hard to predict. Eventually OS would outgrow its designated partition, but the free space from the “data” partition cannot be used.

Tuesday, 3 August 2010

Waterproof or not?

Roaming the web we stumbled upon a blog post that tells about new waterproof SD card technology. Naturally, we wondered whether such memory cards are really needed or may be ordinary cards are just enough. So we gathered memory cards which were at hand and also decided not to ignore a USB pen drive. We formatted and put files on all of them.
Then we filled a microwave container with water, put all the devices into it, and left them sit underwater for half an hour.

So we got (left to right)

  • Nikon EC8-CF 8MB CompactFlash
  • Transcend JetFlash V30 2GB (USB pen drive)
  • Sandisk M2 2GB
  • Kingston MMC mobile 1GB

under water

After that we got the devices out, wiped them dry and connected to the computer one by one.

And here is the result of our experiment: all of the memory cards work well with their content intact. As for the USB pen drive, we were concerned for a moment that we killed as we watched it sink slowly, filling up with water. However, in the end, the pen drive works perfectly as well.

Monday, 2 August 2010

Data recovery after reinstalling Windows yields better results than it can be expected. During the reinstall, the drive is formatted and the new copy of Windows is installed.

If the format was "Complete" and it was Windows Vista/7 that was installing then nothing can be recovered. During the format, Windows Vista and Windows 7 overwrite the drive content with zeros.

If you use the "Quick" format, then Windows will be installed on the clean drive, in the same way as it was installed the first time. Since a computer always produces the same result for the same task, the new copy will be written over the previous copy (except for possible different selection of the components to be installed). Thus the previous Windows files will be overwritten, but not the user files which were written later. Certainly some files will be lost (e.g. data saved in a registry like settings and passwords), but the documents have a good chance to survive a reinstallation.

This approach doesn't work if you are going to install a newer Windows version because new versions have larger size.