Selling Hard Disk Drives on eBay
The market for used and second-hand hard disk drives is always increasing, because drives are getting more reliable and lasting longer, and manufacturers are providing many years of limited warranty.
When selling a hard disk drive whether on eBay or anywhere else, it is usually a good policy to be honest about the drive, because after all, you want customer satisfaction. Many people sell drives with a single line "In good condition". However, what does that mean? Just because the outside metal is shiny does not necessarily mean that it is a good drive.
Definition of a Good and Working Drive
How do you define a good working drive? A computer drive is a complicated piece of electronic engineering. Does simply spinning and making a noise mean it is good, because it is possible to get a drive that spins and formats, yet is totally useless.
If you are an intelligent seller with a number of good working drives that you want to get good money for, then display the S.M.A.R.T. parameters of the drive. Each drive keeps a record of the number of hours it has been used, and the number of errors it has had to correct. It keeps a list of all the errors that have occurred.
If you are a large seller of recycled hard drives, then you should keep a test system where you can connect a drive and get its S.M.A.R.T. parameters. You can find out very quickly if a drive is good, failing, or has failed. This way, when you write that a drive is good, it really is good because you have the S.M.A.R.T. parameters to prove it!
CrystalDiskInfo is a program that displays all the S.M.A.R.T. parameters in a simple way so that almost anyone can understand. Here is a screenshot of a good drive I recently bought.
Sometimes a drive fails slowly and one of the most typical parameters that become highlighted in red is the Reallocated Sectors Count. This usually indicates that the drive has a problem and is failing slowly. In all honesty you cannot say that the drive is good and working, when it is failing slowly, hence honesty is always good.
S.M.A.R.T. parameters are extremely valuable in predicting a hard disk failure. When I was a system administrator I used to keep a weekly log of these parameters, and when a disk appeared to have problems it was replaced with a new one. This is because after the first reallocation error is detected, a drive is 40 times more likely to fail then one without any errors.
Although thse drives have not totally failed, they are considered to be failing, and therefore selling them as good working drives on eBay is not very honest.
It is of course very smart to be able to understand how the parameters work and once you are an expert at it, you can tell at a glance if a disk is going to fail. However if you are not an expert, then there is some really great software on the Internet that can interpret the values for you and highlight the parameters of concern.
Interpreting S.M.A.R.T Parameters
Interpreting these parameters is actually quite simple and just takes some practice. The threshold column shows figures that the manufacturer has set. These figures do not change over the lifetime of the drive, but are there for comparison purposes. The current value is the current measurement of the parameter. The worst value is the worst measurement that parameter has ever recorded over the lifetime of the drive.
Reallocated Sectors Count
The reallocated sectors count is one of the most interesting and useful parameters worth learning. Manufacturers usually anticipate a small number of sectors to fail over the lifetime of the drive, and therefore they set aside a small limited amount of space on the disk, known as reallocation space, for replacing the faulty sectors. This is done by marking the faulty sector as bad and remapping that part of the memory to the reallocation space on the disk. As the number of faulty sectors increase over time, the free reallocation space gets used up. Since this space is limited, once it is used up, the drive can no longer reallocate bad sectors.
For this parameter, the current value and worst value are usually the same, and in a new drive -- depending upon the manufacturer -- their values start out at 255, and drops as the number of reallocated sectors increases. Usually the column marked RAW shows the actual number of reallocated sectors.
The amount of actual space set aside for reallocation is usually a trade secret. However, it is an important metric to have because when the space is used up the drive will no longer be able to reallocate bad sectors. Therefore manufacturers provide this information in a normalised scale form between 255 (space – unused) and 0 (empty – no space left).
The manufacturer also provides a threshold value for this parameter, and when the value in the current column drops below the threshold value then the drive is deemed to have failed. Manufacturers usually perform laboratory tests on the drive to establish this threshold value.
Another reason why they normalise these values into scale between 255 and 0 may be so that it could be fed to a display gauge or passed to other software for graphical display. Since the gauge would display a slowly dropping needle, it more accurately reflects the reduction in reallocation space which drops as the number of bad sectors increase.
As a network administrator, the current value is the one to keep an eye on, because if it starts to drop fast and go below the threshold value, then the drive has failed. When a drive shows a small number of reallocated sectors, and the current value is still above the threshold, then most software recommend "Caution". When the current value drops below the threshold, then most software usually indicate "Fail or Bad".
A failed or failing drive is no longer reliable and cannot be used for storing data, because it is no longer fit for purpose and is usually replaced and disposed.
Here are two seller refurbished drives I bought on eBay. The seller said that they were in good condition, hardly used, and working. He had erased and formatted them and they were ready for use by the next owner. What this really meant was that the metal is shiny and the drives spin when powered up. The S.M.A.R.T attributes of these drives tell much more though.
Example Disk 1
The "Power On Count" and the "Power On Hours" values show that this drive has remained powered for long periods and therefore it was very likely used in a server. The number of hours use indicates it had been powered continuously for approximately five years. The "Reallocated Sectors Count" shows the current and worst values to be 199. The manufacturer has set a threshold value of 140 for this parameter. This means that when the current figure drops below the threshold value, the drive is deemed to have failed. The RAW column shows three sectors to have been reallocated.
As you can see, this is a worn out old drive that has just recently started to show signs of failure. Since this drive has done over 50,000 hours it is likely that this is the prelude to something more serious about to happen.
Example Disk 2
This is another drive I bought from the same seller on eBay. The "Power On Hours" figure shows it has operated for 25,536 hours, and it is another drive used in a server application. The current value of the reallocated sectors count is 130, and well below the threshold value of 140 as set by the manufacturer. Therefore, by the manufacturers reckoning, this drive is no longer fit for purpose and it is a failed drive. The RAW column shows 230 sectors have been reallocated.
Read Error Rate
Here is another dodgy drive I recently bought from a seller who sold it as a new drive. The Power On Count value tells me this drive has been switched ON 1030 times. The Power On Hours value is 12,083 hours, which indicates this drive has been in use for a considerable amount of time.
Additionally, there is the Un-correctable Sector Count flagged with Caution. This means that the drive is unable to reallocate bad sectors for some reason. However if you look at the Read Error Rate, it shows 197 in the worst value, and the raw value is 54. This indicates a likely problem with the read heads. For some reason it has had problems reading, which may be due to dust particles in the drive, or the head has simply started to fail. Either way, you would not expect this of a new drive.
If you are a smart buyer, then the S.M.A.R.T parameters are the first things you would check to make sure you are getting a new drive and to determine whether the drive is fit for data storage purposes.