Resource of SSD disks for servers

The best prices for official DELL PowerEdge R760 servers in Ukraine.

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Available server models from the warehouse in Kyiv:

• Server Dell PowerEdge R760 - Intel Xeon Silver 4510 2.4-4.1Ghz 12 Cores

• Server Dell PowerEdge R760 - Intel Xeon Silver 4514Y 2.0-3.4Ghz 16 Cores

• Server Dell PowerEdge R760 - Intel Xeon Gold 6526Y 2.8-3.9Ghz 16 Cores

• Server Dell PowerEdge R760 - Intel Xeon Gold 5420+ 2.0-4.1Ghz 28 Cores

The lifespan of an SSD based on NAND flash memory is determined by the number of write and erase cycles that the drive can withstand in its life cycle. Regardless of the type of memory, manufacturer, and SSD controller, NAND cell degradation is caused by internal processes such as garbage collection and write amplification. The most effective way to extend the life of solid-state drives is to increase the area of ​​service cells, overprovisioning memory.

Garbage collection ( GC)

NAND memory is divided into blocks, which are divided into pages. It is impossible to write data directly to flash memory at a physical address. The SSD controller writes updated data to free pages, marking the original ones as invalid. The address translator redirects the logical addresses of updates to new physical addresses. It is impossible to erase a page with data that has lost its relevance (garbage), only an entire block can be erased. To free up, make available to the OS the memory space under irrelevant data, you must first move the valid data of the adjacent pages of the block being freed to pages in another block. This is GC, the process of collecting valid data into working blocks with subsequent erasure of garbage.

Write amplification ( WA)

When the SSD fills up and there are few free blocks, each write operation causes a series of data moves by the controller to assemble them into consistent blocks and clear space by garbage collection. As a result, the amount of writing to flash memory cells (including copying real data during GC) can be many times greater than the amount of sending a host write. WA write gain is the ratio of these amounts. It depends on the workload profile. As a rule, random writing of short fragments multiplies writes much more than sequential writing of large ones: random access data is more fragmented, more operations are required to collect scattered small garbage.

Overprovisioning ( OP)

To allow the garbage collector freedom of maneuver, an OP area is allocated from the total SSD memory space, accessible to the SSD controller but inaccessible to the host. This reserve of service NAND memory cells is used as an intermediate field for moving GC data, leveling wear, and replacing broken cells. The SSD manufacturer itself assigns the OP size, reducing the user capacity of the SSD. There are generally accepted denominations (such as 256GB or 240GB), but they can be any:

This explains the diversity of SSDs, when drives on the same controller, but with different passport indicators, come out of the hands of the same vendor.

The logic of OP marking is easy to imagine using the example of a game of "tic-tac-toe". If there were more than one free cell on the field (for example, a 5x5 box instead of a 4x4), the same dice from 1 to 15 could be arranged in fewer moves. The same is true with SSD write enhancement: the larger the service reserve, the smaller it is.

Cell wear

The user is not interested in the mechanics of the process, but in the forecast of SSD survivability - in terms of daily write volumes (DWPD) or, more correctly, total write volumes during the life cycle (TBW). The average statistical resistance to wear (endurance), which we see in SSD passports, is calculated according to JEDEC standards. For server drives - on corporate templates with random access loads.

The TBW prediction increases with increasing OP, but not linearly. From a certain point, adding OP does not lead to a noticeable increase in resource, but rather reduces SSD throughput. The appropriate size of the reserve area for actual use is selected by assessing the nature and intensity of loads, including in similar tasks on old servers.

Productivity SSD

Random write performance is at its peak on a fresh drive. As the drive fills up, data becomes increasingly fragmented, and the SSD controller spends more time on garbage collection, which is the main factor in performance degradation. Increasing OP reduces WA, the controller frees pages for writes faster, and promptly processes host requests when the SSD is close to saturation with writes.

Everything is in the hands of the user

The size of the OP is not a permanent property of the SSD, an insurmountable obstacle to resource management and performance. All major vendors have utilities that allow you to control various SSD parameters. Including changing the size of the service cell area of ​​server drives - just like it is done at the factory.

• Overprovisioning is the practice of reducing the usable capacity of an SSD to increase its resource and performance. Overprovisioning is set by the Host Protected Area (HPA) parameter.
• This feature is only supported by Kingston Data Center series SSDs.
• First, delete all partitions on the SSD. Wipe the SSD using diskpart. Secure erase is recommended for better performance.
• Enter the desired capacity in gigabytes (GB) and the last four digits of the SSD serial number. After modifying the HPA and rebooting, the system will recognize the new drive capacity.

Know the measure.

Software tools for managing SSD resources and performance increase user freedom – a valuable quality in times of poor availability of various storage capacities. Instead of waiting a long time for exotic Write Intensive SSDs (5-10 DWPD) to be delivered, it is enough to buy affordable Mixed Use (1-3 DWPD) and mark them for a smaller capacity.

The optimal size of the OP depends on the application. For workloads with intensive random access writes, it is beneficial to sacrifice some capacity for increased lifetime and performance gains. Where reads predominate, wastefulness is inappropriate.

How can we help?

Server Solutions sells Dell PowerEdge R760 and Dell PowerEdge R760xs servers throughout Ukraine, our clients include small, medium and large businesses. If you or your company needs advice and the purchase of quality server equipment, then you should contact us.