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Is your SSD really that fast?


The SSD should ensure high speed. But for this advantage to be achieved, certain requirements have to be met. But your SSD is probably not as fast as you think. Of course, the flash memory works faster than a hard drive. But if you bought a new computer with an SSD or freshly installed Windows 10 on the flash drive when you switched, the perceived speed plus is mainly due to the uncluttered system. The high data rates that manufacturers promise for their drives are almost never achieved by an SSD in practice. But with the right test tools and the knowledge of what influences the SSD speed, you can quickly find out whether your flash drive is slowing you down in your PC or whether it is really worth buying a new SSD.


The SSD technology ensures a high speed
How fast your SSD actually works in the computer depends on what you are doing on the computer. Because as with the processor or memory, there are tasks that the SSD can do immediately at high speed. Others, on the other hand, demand them in such a way that their pace drops significantly. For technical reasons, an SSD can read data faster than write it, and the longer the flash disk is in use, the greater the difference between the read and write performance. Because the SSD controller can only write directly to empty memory cells: If information is already in a cell, it must delete it and, if necessary, write it to another area before it can carry out the write process. The more storage space is used on the SSD, the fewer free cells are available.

 

The best SSDs in the terabyte class
That is why the manufacturers provide their SSD with various functions that should ensure that there is always enough space free. This not only keeps the writing speed high, but also extends the service life of the SSD, since memory cells can only cope with a certain number of write processes. Over-provisioning, for example, does not make part of the SSD capacity available to the operating system and this is why Windows often shows less storage space than the SSD has according to the manufacturer. However, the controller can use these cells for write operations. Depending on the SSD model, this reserved part is between six and around 30 percent. With a manufacturer tool, Samsung Magician, check whether and how much space your SSD has ready for it.

The Windows Trim command also provides more free cells: The operating system uses this to tell the drive which files it no longer needs. The SSD controller can then delete the corresponding cells in advance as part of its clean-up work (garbage collection) so that they are available during a write process. This takes place while the SSD is idle in order not to slow down read or write actions. Current operating systems use this command automatically; Check whether it is switched on in Windows 10 with the command line: 

Quote

fsutil behavior query disabledeletenotify

If the answer is "= 0 (disabled)", Windows uses the command. In addition, the SSD Trim must understand what the manufacturer's tool or an SSD checker such as Crystaldiskinfo or Hard Disk Sentinel shows. With an older SSD, a firmware update or a manufacturer driver may help that the drive can handle Trim.

 

How used space affects speed
SSDs often hold part of the storage space via over-provisioning (OP) so that the controller always has free cells for writing. The manufacturer's tool tells you how much capacity your flash drive uses for this. With an SSD with more storage capacity, if you use it for a longer period of time, the chances are better that the controller will find unoccupied cells and the write performance will remain stable. But it also ensures more speed because there are more memory chips on it: the controller can address these in parallel and handle more processes at the same time provided it has a correspondingly many memory channels. This is especially the case with NVMe SSDs, because this access protocol makes it easier to manage parallel accesses.

In normal PC operation, an SSD normally reads significantly more data than it writes. So you don't have to worry about low write performance, provided you use your computer like most users. You can find out by checking the relationship between read and write operations on your SSD: This is what the Hard Disk Sentinel program tells you, for example. If you click on the “Drive performance” tab, the first two lines will show you the read and write performance of your SSD since the program was started and the program was installed. Also the freeware Disk Counters View informs you about read and write processes as well as the amount of files transferred.

Both programs get the information from diskperf, which Windows automatically activates in order to log the performance of the drives. The relationship between read and write processes can also be found using the smart values "Total LBAs Written" and "Total LBAs Read": However, smart tools such as Crystaldiskinfo can only display these when they output the SSD, but mostly you only see the value for the written blocks “Total LBAs Written”.

Windows uses a trim command to tell the SSD which memory cells the controller can safely delete.  You can use a tool or command line input to determine whether Trim is active on your system. With the smart values “Wear Leveling Count” and “Used Reserved Block Count”, you can keep an eye on the number of free or reserved memory cells: Most tools indicate the optimal status with a value of 100. The further it is reduced, the fewer cells are available to the controller for write operations. However, these individual values are more of an informational nature. If the number of free cells reaches a critical value, the tool gives you a more noticeable hint, for example Crystaldiskinfo about "overall condition". 

 

Fast for large files, slow for small ones
Normally an SSD in a Windows computer has to read more than write.  Analysis tools such as HD Sentinel show what the read / write ratio is doing in your system. The speed an SSD delivers in practice also depends on the size of the files it transfers, especially when writing. This is because the flash memory is organized in memory blocks of 512 KB, which again consist of so-called pages of 4 KB each. In order to write to a page, the SSD must first delete the entire block or move it to another storage location. This happens very quickly if the controller has to write a large file because it then deletes or moves entire blocks. With smaller file volumes, the effort is correspondingly greater and the writing speed is lower. That is why an SSD delivers the highest speed, for example when copying videos or an ISO file. On the other hand, if you copy a large number of small files, the flash memory will work significantly slower.

Even if a write process takes a long time, for example because you are copying a large folder, the performance of the SSD can decrease. This also happens when there is little free space left. Most SSDs use an internal cache to achieve high transfer rates: This consists of SLC memory cells that can be written to more quickly than TLC or QLC memories, which most SSDs use. If all SLC cells are filled during a longer write access, the controller has to fall back on the slower memory cells, which slows down the SSD. When this happens depends on how big the cache is on your SSD and how much storage space is still free: For many SSDs, the size of the SLC cache depends on this, because it offers less storage capacity than TLC or QLC storage.

You should find out how big the cache of a certain model is in the technical data: However, many manufacturers hide this information behind marketing names such as Turbo-Write (Samsung) or Dynamic Write Acceleration (Crucial). Heat can also slow down the speed of the SSD: With very fast SSDs and long data transfers, the SSD controller can heat up so much that it throttles the transfer rate. You should therefore make sure that the PC fans also cool the SSD sufficiently. Heat can also slow down the speed of the SSD: With very fast SSDs and long data transfers, the SSD controller can heat up so much that it throttles the transfer rate. You should therefore make sure that the PC fans also cool the SSD sufficiently. Heat can also slow down the speed of the SSD: In the case of very fast SSDs and long data transfers, the SSD controller can heat up so much that it throttles the transfer rate. You should therefore make sure that the PC fans also cool the SSD sufficiently.

 

This is how you can easily test the practical speed of your SSD
An SSD only delivers maximum speed when it is in an optimal condition: Analysis tools regularly check the general SSD status and provide information on problems. You can use free test programs to check how well your SSD suits your PC usage. In addition to professional benchmarks, these are also used in many SSD tests: When choosing a new model, you can not only pay attention to its technical data, but also to certain test results that are important for your daily PC work.

In the standard settings, Crystaldiskmark 7 checks the sequential read and write rate of an SSD in the first two tests SEQ1MQ8T1 and SEQ1MQ1T1. The other two tests, RND4KQ32T16 and RND4KQ1T1 determine the transfer performance for distributed and random access. The tool displays the results as a transfer rate in MB per second. In many tests you will also find the result IOPS (Input/Output Operations per second): It describes how many read or write commands the SSD can execute in one second. Above all, this should better map the performance of random accesses, where it is less a matter of how much data volume the SSD transfers, but rather that it does it particularly quickly. With Crystaldiskmark you can see the result for each test in IOPS when you move the mouse pointer over it.

You can find out in Crystaldiskinfo whether the SSD or its controller heats up too much during operation.  If that is the case, you should ensure better cooling. In every test, however, the SSD performance always relates to the file or files it is supposed to read or write and therefore depends on the file size and the file system. In Crystaldiskmark, set the size of the test files using the second drop-down menu from the left, the tool uses 1 gigabyte by default. With a larger file, you can, for example, check whether the SSD cache is full and therefore the transfer rate is reduced, or whether thermal problems come into play due to the longer read / write process.

The test name, for example SEQ1MQ8T1 - also reveals how the test file is divided: In the example, "1M" stands for file blocks of 1 MB. In the distributed tests, the tool uses 4 KB blocks, which corresponds to the usual cluster size of the NTFS file system. The number after Q stands for Queue Depth: This is how many requirements a system process, for example a program, places on the SSD at the same time. The number of processes that want something from the SSD in parallel is indicated by the T, which stands for "threads". Depending on its technical equipment, an SSD benefits from a high query depth and thread count, since the controller can rearrange the incoming commands for faster processing and distribute them over several storage channels.

Reading is easier for an SSD than writing, it can process large files faster than small file blocks: Crystaldiskmark therefore checks the speed in four tests with different requirements. With Crystaldiskmark, an SSD usually achieves the best values in the first and the lowest data rates in the fourth test. Because sequential reading is easiest for a flash memory. Combined with the high query depth of eight queues, NVMe SSDs in particular use almost the maximum bandwidth of the interface, for example, almost 4 GB/s with PCI-Express 3.0 x4. This also applies to the write rate depending on the SSD fill level. The manufacturers also advertise with these values, but this test has at least to do with daily PC use. An SSD only achieves such data rates if you play a large, locally stored video file or copy an ISO file provided the source or target drive is at least as powerful.

With Crystaldiskmark you can use various test profiles to check whether the SSD in your computer is delivering the optimal speed for your usage behavior. The settings can be found under "Profiles". Most of all, the SSD in a Windows PC deals with random read and write requests: When the operating system and programs start, the flash memory has to read and sometimes write 4K blocks quickly. Even when multitasking, for example when you are editing a Word document, watching a video at the same time and the virus scanner is checking in the background at the same time, the performance of distributed requests for small files is crucial. That is why the results in the fourth test by Crystaldiskmark are usually the lowest, but most close to the practical speed of an SSD under Windows 10.

 

PC Mark 10: Practical, but expensive
Like most other free tools, Crystaldiskmark does not use real programs for the SSD test. The storage benchmark of PCMark 10 is more practical: That is missing in the free basic edition of the test program and is only included in the professional edition, which costs around 1500 dollars. This is why editors in particular use it for their tests. Many office also uses it for SSD tests on notebooks.

The benchmark uses ready-made program sequences, for example the start of Windows 10 and programs such as Adobe Photoshop and games, and simulates, among other things, copy actions with large ISO files and many small photo files. This mixture simulates very realistically the tasks of an SSD in a private user's computer. It records the performance of the flash drive in an overall result in points, which is calculated from the determined data rate and the access time. In this test, SSDs with a fast cache memory, such as the drives from Intel, do very well, which usually bring up the rear in the sequential data rate and in tests with high query depth

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