Over provisioning vs write amplification

Cheers, -- Cirt talk According to the formula in the article itself, that would mean that the drive stores only half of the bytes given to it by the operation system. In other worse, according to the formula in the article, the drive is losing half the information which clearly is not a good feature. The claim is deceptive if it is done by using compression since compression is a concept that is orthogonal to write amplification and should not be counted when calculating write amplification.

Over provisioning vs write amplification

Talk:Write amplification - Wikipedia

About all I can see is a "model number" e. I think you mean "[hypothetical] I have no discipline, need my system to push back against continued abuse, and have no software to set a high water mark alarm".

Which is a perfectly valid criticism, albeit interesting from someone who would consider over-provisioning in the first place. However, there are still situations, primarily in datacenter environments, where over provisioning vs write amplification is recommended.

over provisioning vs write amplification

To understand why overprovisioning can be useful, it is necessary to understand how SSDs work. Unlike hard drives, NAND cells containing data cannot be directly overwritten; the drive needs to erase existing data before it can write new data.

NAND also has a limited amount of write endurance. To avoid rewriting data unnecessarily in order to erase blocks, and to ensure that no block receives a disproportionate number of writesthe drive tries to spread out writes, especially small random writes, to different blocks.

If the writes replace old data, it marks the old pages as invalid. Once all the pages in a block are marked invalid, the drive is free to erase it without having to rewrite valid data. SSDs need free space to function optimally, but not every workload is conducive to maintaining free space If the drive has little or no free space remaining, it will not be able to spread out writes.

Instead, the drive will need to erase blocks right away as writes are sent to the drive, rewriting any valid data within those blocks into other blocks. This results in more data being written to the NAND than is sent to the drive, a phenomenon known as write amplification.

Write amplification is especially pronounced with random write-intensive workloads, such as online transaction processing OLTPand needs to be kept to a minimum because it results in reduced performance and endurance.

over provisioning vs write amplification

To reduce write amplification, most modern systems support a command called TRIMwhich tells the drive which blocks no longer contain valid data so they can be erased. However, TRIM is sometimes not possible, such as when the drive is in an external enclosure most enclosures do not support TRIM or when the drive is used with an older operating system.

Furthermore, under highly-intensive random-write workloads, writes will be spread over large regions of the underlying NAND, which means that forced rewriting of data and attendant write amplification can occur even if the drive is not nearly full. Modern SSDs experience significantly less write amplification than older drives but some workloads can still benefit from overprovisioning The earliest SSDs had much less mature firmware that would tend to rewrite data much more often than necessary.

Early Indilinx and JMicron controllers the JMF was infamous for stuttering and abysmal random write performance suffered from extremely high write amplification under intensive random-write workloads, sometimes exceeding x.

Newer controllers, with the benefit of higher processing power, improved flash management algorithms, and TRIM support, are much better able to handle these situations, although heavy random-write workloads can still cause write amplification in excess of 10x in modern SSDs.

Overprovisioning provides the drive with a larger region of free space to handle random writes and avoid forced rewriting of data. For example, you can partition a GB SSD to GB and leave the remaining space unallocated, and the drive will use the unallocated space as spare space.

SSD Extra Over-provisioning - QNAP

Do note, however, that this unallocated space must be trimmed if it has been written to before; otherwise, it will have no benefit as the drive will see that space as occupied.You just read: Storbyte Solves The 'Garbage Collection', 'Write-Cliff', 'Write Amplification', 'Over Provisioning' Solid-State Storage Problem.

Furthermore, under highly-intensive random-write workloads, writes will be spread over large regions of the underlying NAND, which means that forced rewriting of data and attendant write amplification can occur even if the drive is not nearly full.

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.

For example, as the amount of over-provisioning increases, the write amplification decreases (inverse relationship). If the factor is a toggle (enabled or disabled) function then it has either a positive or negative relationship.

For example, as the amount of over-provisioning increases, the write amplification decreases (inverse relationship). If the factor is a toggle (enabled or disabled) function then it has either a positive or negative relationship.

This is not over-provisioning per se, but instead the OS is telling the controller that space is unused and need not be preserved thus reducing write-amplification. A result similar to what over-provisioning achieves, but not actual over-provisioning.

SSD | Understanding over-provisioning