Test example・Deterioration test of secondary storage devices such as flash memory and HDD
- 1. It is important to check the operation of secondary storage devices such as flash memory and HDD when they deteriorate.
- 2. Why are flash memories and HDDs called secondary storage devices?
- 3. Why flash memory and HDD deteriorate
- 4. What happens when flash memory or HDD deteriorates
- 5. How to perform a secondary memory degradation test
- 6. Next to the secondary memory degradation test is the high load aging test
It is important to check the operation of secondary storage devices such as flash memory and HDD when they deteriorate.
Large-capacity secondary storage devices such as large-capacity flash memory and hard disks are often used for embedded software . As a result of increasing the storage density on the storage medium for both flash memory and hard disk in order to realize a large capacity, the rate of error occurrence and information loss due to deterioration has increased.
In particular, flash memory has become larger in capacity and lower in price , so depending on the conditions of use , information may deteriorate in less than a month . Therefore, even as a test before the release of embedded software, it is becoming more important to check the operation when the secondary storage device deteriorates . This article provides an overview of secondary storage degradation and the corresponding tests.
Why are flash memories and HDDs called secondary storage devices?
By the way, what is a secondary storage device ? Before proceeding, I would like to briefly introduce the secondary storage device. A computer realizes various processing by reading, processing, and recording data by a CPU (Central Processing Unit). The place where this data is stored is the memory device . The types of this storage device are classified into temporary storage device / secondary storage device / tertiary storage device in order from the CPU . There is no clear definition for primary storage / secondary / tertiary storage, but the following classifications are commonly used.
1 Storage device : A storage device that is connected to the same circuit as the CPU (actually, a data communication path called an internal bus) and can be accessed at high speed. It often refers to memory typified by DRAM (cache memory in the CPU is often not called primary memory). High quick-access is advantageous as possible the cost of capacity Atari high Noto power is turned off when the information is lost is disadvantage.
Secondary storage device : A low-speed but large-capacity storage device that is connected to the CPU via an external interface circuit. It often refers to flash memory and HDD including SD cards and SSDs . It has the advantage that information is maintained even when the power is turned off, but it has the disadvantage that the access speed is slower than that of a temporary storage device .
Tertiary storage device : A storage device that is provided in a housing separate from the computer body and can provide a large capacity by exchanging storage media, and is sometimes called an external storage device. It often refers to rewritable DVDs and CDs , removable HDDs , and magnetic tape devices , which are rarely seen these days . It has the advantage of being able to store a very large amount of memory, but has the disadvantage of taking a very long time to access the removed storage device .
Each has its advantages and disadvantages, so at the stage of designing the architecture of a computer system, it is decided what kind of storage device to use.
Why flash memory and HDD deteriorate
The main point of this article is that testing is important because flash memory and HDD deteriorate, but why does it deteriorate in the first place ? Flash memory and HDD have the advantage that information can be maintained even when the power is turned off , but if it is flash memory, it is the amount of charge stored in the internal electronic circuit, and if it is HDD, it is the amount of charge stored in the internal electronic circuit. Information of 0 and 1 is stored by the orientation of a minute magnet on the storage medium. by .
However, as time goes by, the electric charge for storing this information decreases, and the direction of minute magnets changes, so that the stored information is lost, which is the main cause of deterioration. This loss of information, because it depends on the mechanism of the storage of flash memory and HDD, extent there would occur at a rate of degree can not be avoided is. Of course, if information is lost, it will not be useful as a secondary recording device, so flash memory and HDD have a built-in function to recover lost information in various ways .
However, these functions are not all-purpose, and if more information is lost, it will take time to recover or it will not be possible to recover . As a result, the deterioration of the secondary storage device is that the access performance deteriorates and the stored information is lost . This deterioration of the secondary storage device requires special attention for large-capacity flash memory, which has been increasingly used recently. In flash memory, data loss is accelerated by increasing the number of readings and writings and increasing the temperature . Due to the recent increase in capacity due to high integration, some types of flash memory have deteriorated in a fairly short period of time.
For example, there is a “product specification" flash memory that loses the written data in 9 days if the temperature is 60 degrees after 3,000 rewrites . To avoid misunderstanding, this is a product specification, so it is not a problem. If the temperature is 30 degrees, it will not deteriorate for a year, so it can be used sufficiently depending on the application. However, it is important to carry out tests assuming that deterioration will occur during use. HDDs do not deteriorate for such a short time, but if they are operated at high temperatures, data will be lost due to deterioration on a yearly basis.
What happens when flash memory or HDD deteriorates
Even if the flash memory or HDD has started to deteriorate , in most cases, the built-in error repair function works, so the data will not be lost on the surface . Even to the extent that can not be recovered by the error repair function disappears large amounts of data progressed deterioration and so, on the surface be read can not be read out the data in real-out error state will begin to occur. Deterioration of flash memory and HDD roughly proceeds in the following three stages.
- First stage (no deterioration): Most recording elements are recording data normally
- Second stage (deterioration start): Data is lost in some storage elements, but the data is recovered by the internal error repair function.
- Third stage (expansion of deterioration): Data is lost in many storage elements, and there is an area that cannot be recovered even by the error repair function.
In the second stage , the written data can be read properly, but since the error repair function is operating internally, it takes a lot of time to read the data, and it may appear as a decrease in access speed. It is often there. Therefore, in the test, the operation of software error handling in the second and third stages is mainly confirmed by the semi-normal system test.
How to perform a secondary memory degradation test
Such as a flash memory or HDD verify the operation of the error processing in a state in which the secondary recording device is degraded in order to, quasi-normal system test of it is I need, this is when viewed from the built-in software hardware error has occurred It is difficult to carry out because it corresponds to the test when you are doing it . In order to execute the test, it is necessary to actually extend the response time from the flash memory or HDD , return a read error response to the read command, or return a write failure response to the write command. Become.
If you are a manufacturer of flash memory or HDD, you can also prepare a test device that simulates such abnormal operation, or a flash memory or HDD that incorporates special firmware that returns an error response exclusively for testing . However, it is often difficult for an ordinary embedded software development company to prepare for that.
Then, what to do is that the story is simple, and you should bring the flash memory or HDD to the point of being damaged and destroyed . Since the storage medium of both flash memory and HDD is sensitive to temperature, if you repeat reading and writing at 60 or 70 degrees for several days, the storage element will eventually become worn out and deterioration will begin to occur. When the deterioration progresses appropriately, use the flash memory or HDD as a tool for the deterioration test of the secondary storage device . Although it is not possible to create a very accurate deterioration status, the behavior itself when the actual flash memory or HDD deteriorates can occur, so it is sufficiently effective as a test for embedded software.
Next to the secondary memory degradation test is the high load aging test
Due to the large capacity and high density of secondary storage devices such as flash memory and HDD, the possibility of deterioration in actual operation situations has increased, so in this article we will discuss the test of semi-normal processing to deal with it. I introduced it. It is necessary to check the operation of various quasi-normal systems for stable operation of embedded software. In the next article, I will introduce the quasi-normal system test by high load aging.