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How many write cycles with the stick?
In comments to the story about the causes gradual degradation of flash drives our readers are interested in, how long will elaborate stick. The answer to this question depends on including the number of write cycles to the flash drive. Bressers blogger Josh (Josh Bressers) decided to study the matter thoroughly and conducted testing, during which he checked the flash drive endurance. The results surprised him: stick was much stronger than anticipated. The actions described below are not recommended to be repeated, since the purpose of the testing was to test the strength of the stick. And it can be done in only one way: to bring her down.
The experiment was conducted on the memory stick Sony Microvault USB Flash Drive with a capacity of 1 GB. It is important to understand that different flash drives will behave differently. This depends on many factors, some of which were previously discussed in our life.
Testing flash endurance
Тестирование флешки на выносливость
To test Bressers Josh wrote a utility that uses the sign O_DIRECT. It is possible to access the file system directly to the file. It is preferred that the file system to cache data in memory. How does caching, our readers already know , so this time we will do without details.
In most cases, caching is the best solution, but for the problems of this test, it was not appropriate because the strength of the flash drive is checked. Should treat each time it is to her, and not to the RAM. To use O_DIRECT, the stick had to reformat the file system ext3. Initially, it was supplied with the file system vfat, which is not characterized by the ability to work correctly with a sign O_DIRECT.
The file system was created as follows:
mkfs.ext3-m 0-b 1024 / dev/sdb1
Preparation for the experiment was over and began self testing.
First drive was completely filled with data, leaving only one free block. It was supposed to write in it more and more data as long as the flash drive does not fail. Create test file was carried out as follows:
dd if = / dev / urandom of = test-file bs = 1024 count = 1
Filling the drive was carried out the following commands:
dd if = / dev / urandom of = big-file
This was followed by tests performed by the application, overwriting the file test as long as the flash drive is not denied.
It was found that a small block. Josh Bressers himself does not know the reasons for this phenomenon. This particular file system. For this test, it took three free blocks on a flash drive.
Josh Bressers believed that the flash drive will sustain approximately 30,000 write cycles. That is about 10,000 write cycles in each block.
The test results
The graphs (hereinafter) illustrating a process of testing time is given in microseconds and the number of cycles in thousands of cycles.
Flash refused after the data has been written into it 90,593,000 104 times. Her stamina repeatedly surpassed expectations. On the implementation of each of most of the write cycle time of approximately 1 000 500 microseconds (millionths of a second).
The graph shows that from time to time came the “long” write cycle: duration of more than 10,000 microseconds. Apparently, the flash drive is “felt” and that soon will not stand much hard work and began to slow down the speed of each cycle. In this case, the reading speed remained the same.
The end came a flash drive during a write cycle, rather than reading. Terminal (console) issued the following error message:
Message from syslogd @ link at May 15 7:44:03 …
kernel: journal commit I / O error
Interestingly, the computer still continued to “see” the drive and allows you to read information from it, refusing to just write. Josh Bressers involves a substantial likelihood that the flash drive retains the ability to read data from it even after it has become unfit for the record. That is, the probability of data loss is lower than the loss of ability to write.
However, it can only be a probability. There is no certainty in such cases, and there can not be. Note that the above described results of testing a specific instance of a well-defined model of the flash drive.
Other experts believe that the flash drive is able to withstand approximately one million write cycles, or delete data.
According to the materials bress.net
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Tags: External Hard Drives , Flash Memory , Flash .
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