Write amplification calculation formula

Flash memory write cycles

Calculating write amplification Write Amplification is fundamentally the result of data written to the flash memory divided by data written by the host. The two key ways to expand free space thereby decreasing WA are to 1 increase over provisioning and 2 keep more storage space free if you have TRIM support. This step is often completed with IOMeter, VDbench, or other programs that can send large measurable quantities of data. Start writing sequential data to the SSD, noting how much data is being written. Please update this article to reflect recent events or newly available information. In order to be accessible later, data files and their associated location metadata must be completely written to the media before power to the system is turned off. Once the blocks are all written once, garbage collection will begin and the performance will be gated by the speed and efficiency of that process. With a data-reduction SSD, the lower the entropy of the data coming from the host computer, the less the SSD has to write to the flash memory, leaving more space for over provisioning. The result is the SSD will have more free space enabling lower write amplification and higher performance.

To match that attribute, take the number of times you wrote to the entire SSD and multiply by the physical capacity of the flash. The portion of the user capacity which is free from user data either already TRIMed or never written in the first place will look the same as over-provisioning space until the user saves new data to the SSD.

We call this undesirable effect write amplification WA.

Write amplification rocksdb

SSDs without data reduction technology do not benefit from entropy, so the level of entropy used on them does not matter. With sequential writes, generally all the data in the pages of the block becomes invalid at the same time. Although you can manually recreate this condition with a secure erase, the cost is an additional write cycle, which defeats the purpose. In the case of over provisioning, more is better, since a key attribute of SSD is performance. We know that under normal conditions, an SSD will have a WA very close to when writing data sequentially. This requires even more time to write the data from the host. Because data reduction technology can send less data to the flash than the host originally sent to the SSD, the typical write amplification factor falls below 1.

When data reduction technology sends data to the flash memory, it uses some form of data de-duplication, compression, or data differencing to rearrange the information and use fewer bytes overall. They simply zeroize and generate a new random encryption key each time a secure erase is done.

Once you understand how WA works and how to measure it, you will be better armed to defend yourself against this beastly cause of degraded SSD performance.

Ssd garbage collection

His more than 25 years of marketing and management experience in computer storage and high-technology includes senior management positions at companies including Adaptec, Acer, Polycom, Quantum and SiliconStor. It will take a number of passes of writing data and garbage collecting before those spaces are consolidated to show improved performance. Related Reads. This additional space enables write operations to complete faster, which translates not only into a higher write speed at the host computer but also into lower power use because flash memory draws power only while reading or writing. Although you can manually recreate this condition with a secure erase, the cost is an additional write cycle, which defeats the purpose. You might also find an attribute that is counting the number of gigabytes GBs of data written from the host. Modern hard disk drives now also store error correcting codes ECC within each sector in order to assure data accuracy. Protect your SSD against degraded performance The key point to remember is that write amplification is the enemy of flash memory performance and endurance, and therefore the users of SSDs. At the end of the test period, print out the SMART attributes again and look for all attributes that have a different value than at the start of the test. With a data-reduction SSD, the lower the entropy of the data coming from the host computer, the less the SSD has to write to the flash memory, leaving more space for over provisioning.

A database operates much like a file system in that it uses metadata to track user data. Start writing sequential data to the SSD, noting how much data is being written.

write amplification database

Further information: Trim computing TRIM is a SATA command that enables the operating system to tell an SSD which blocks of previously saved data are no longer needed as a result of file deletions or volume formatting.

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What is write amplification factor (WAF)?