One of the basic data recovery rules is to verify the recovered data

Most data recovery tutorials insist on verifying the recovered data, but usually most people ignore it. So the following scenario may happen:

1. you recover files and the folder tree seems good enough,
2. the disk is formatted or disk data is destroyed some other way,
3. then you see that the restored data is not recovered properly.

It is evident you need to restore disk content once again. Unfortunately, the original hard disk content does no longer exist.

To sum up the above - it is needed to verify the extracted data first and only then begin to fill the original disk with new files.

When you should benchmark your hard drive?

If you think that your storage device is slow, first step is to check linear read speed, disk access time, and IOPS for the device.
Any benchmark software can give you all the mentioned performance characteristics. Searched the web, I saw both paid and free tools to benchmark data storage devices. I used non paid and simple benchmark software - BenchMe - which gives linear read speed in real time. The free benchmark tool also produces a chart with distribution of access time measured for the data storage device.

On top of that, BenchMe free benchmark software provides a list of features the data storage device supports. It is worth to visit the vendor site to have a look at sample benchmark charts for RAID arrays, SSDs, and hard drives. The only minus I 've come across is that the tool doesn't handle hard disks connected via USB.

www.un-erase.com

Finally online. Behold www.un-erase.com.
Still missing adverts, hehe.

RAID 1 array is able to improve average access time

In theory at least, RAID1 can improve average access time (but not random access time) during the read.
This defies widely-held belief that RAID array cannot reduce access time.

RAID1 has two disks with two identical copies of data. If read operations are organized as follows:

• first member disk serves the read operations to the first half of the disk,
• the second disk handles the second part of the data,

then the average length which a read head should travel to locate a sector is reduced by the factor of two.
Based on the above it is not possible to improve rotational latency. In any case, performance increases since less head travel is needed.
In RAID 1 there is no improvement on writes since both member disks should be synchronized.

Why it is critical to read data off both disks in mirror?

A few know that in an implementation of RAID 1 is required to read data off the second disk as well. Otherwise one or even several bad sectors may appear on the second disk of the mirror.

In this situation your RAID 1 doesn't have redundancy any more and you do not know it, contrary to the principle of monitoring the array status. There may be a similar problem with hot spare drives.

One of the causes of this problem is the array being idle most of the time. To make sure the array is still redundant you can read sectors from both disks and compare it. If your RAID operates principally under heavy load you do not encounter such a issue.

In Windows, at least in server versions up to and including Windows 2003, software RAID 1 in most cases reads from the first hard drive, rendering Windows RAID1 arrays unreliable

Hot spare is a handy option, but...

 It is very good to have a hot spare drive, but the hard drive used as a hotspare ought to be tested every now and then.

 Suppose you build your own RAID array and assign N hard drives (including the hot spare disk) to the array. Surprisingly there exists 1/N probability that exactly the disk which is designated to be a hotspare will be the first failed disk. And now you no longer have a hot spare.

 If one of the array member disks fails you find out that the hot spare disk has already failed. To avoid this you need to scan a hot spare on a regular basis or stick to RAID6E or RAID 5E/EE layout.

Before building an array

When building a massive-capacity storage system, take into account the following concerns:

• needed size
• redundancy
• performance
• array cost

Once you have considered points listed in this post it is needed to decide if you need to build your own storage unit or just order ready-made storage. If your choice is the latter option then have a look at this one of RAID Tips. If you decide to build your own storage then review the entire lot on www.raidtips.com.