In South Korea's CN2 server applications, the write speed of solid-state drives (SSDs) may gradually decrease. Initially, they may maintain write speeds of hundreds of MB/s, but over time, speeds may drop to tens or even single-digit MB/s. This phenomenon not only affects data storage efficiency but can also slow down overall business operations, especially in applications that frequently write to databases, logging systems, or those with high concurrency. A comprehensive approach, focusing on hardware features, operating system settings, and application-layer optimization, can be used to gradually troubleshoot and identify appropriate fixes.

Understanding the underlying cause of SSD write speed degradation is crucial. Unlike traditional mechanical hard drives, SSDs rely on flash memory cells to write data. The characteristics of flash memory require an erase process before any write operations can occur. When a drive is first used, the memory cells are empty, resulting in faster write speeds. However, as data is repeatedly written and deleted, the available blocks in the SSD gradually decrease, forcing the controller to perform "write amplification," where writing a single piece of data requires moving or erasing more older data, significantly reducing speed. Furthermore, if the TRIM command is not enabled, the operating system will not immediately notify the SSD controller to release the corresponding storage units after deleting files, causing the hard drive to believe these units are still occupied, further degrading performance.

To address this issue, first confirm whether TRIM support is enabled on the Korean CN2 server's operating system. In a Linux environment, you can test this by executing the following command:

sudo fstrim -v /

If the system returns the amount of freed space, TRIM is enabled. If an error message is displayed, you need to manually configure it. A common approach is to add the discard option when mounting the partition, or to schedule a scheduled task to execute the fstrim command periodically. For example, you can add the following to your crontab:

0 2 * * * /sbin/fstrim -a

This will automatically perform garbage collection on all mounted SSDs every morning, ensuring long-term stable write performance.

In addition to TRIM, you should also pay attention to the I/O scheduler you choose. The default Linux I/O scheduler is often cfq, which is suitable for mechanical hard drives. For SSDs, it is recommended to switch to noop or deadline to reduce unnecessary queueing and waiting. In Ubuntu or Debian, you can modify the setting as follows:

echo deadline | sudo tee /sys/block/sda/queue/scheduler

In CentOS, you can permanently enable the setting by modifying the /etc/default/grub file and updating the grub configuration. A scheduler more suitable for SSDs can reduce system intervention in I/O, directly leveraging the SSD's inherent high concurrency and improving write efficiency.

Another common cause is server disk overutilization. When an SSD exceeds 80% capacity, write speeds drop significantly because the controller must perform more data movement to find available blocks. The solution to this problem is to always ensure a certain amount of free space on the disk. In practice, reserve 10% to 20% of the SSD's unallocated space. The SSD controller will use this area as a backup, ensuring sufficient free blocks for writes. Some enterprise-class SSDs also support manual over-provisioning, using the manufacturer's tools to allocate a portion of space as a hidden area, further improving performance and lifespan.

During server operation, slow write speeds may also be related to the file system selected. Different file systems have varying levels of support for SSDs. For example, ext4 performs more stably with TRIM and delayed allocation enabled, while xfs is more effective at handling large files. If the server frequently writes a large number of small files, it is recommended to use ext4 with the journal_async_commit option enabled to reduce the write burden on the journal system. For big data or video applications, consider xfs or even the more lightweight f2fs file system. Choosing the right file system can reduce unnecessary write overhead at the application layer.

On CN2 servers in Korea, network performance is often the focus, but kernel parameter tuning is equally important when it comes to SSD write performance. For example, adjusting the vm.swappiness value can control the ratio of memory to swap space usage, preventing the system from over-relying on swap writes to disk, thereby improving overall write speeds. You can modify this using the following command:

sudo sysctl -w vm.swappiness=10

Also, you can optimize the vm.dirty_ratio and vm.dirty_background_ratio parameters to reduce the frequency of overly rapid flushing of memory cache data to disk, replacing frequent small-block writes with batch writes, thereby improving SSD lifespan and performance.

In addition to software-level optimizations, poor application design on the server can also lead to rapid SSD performance degradation. For example, frequent log writes without any restrictions, or the database not enabling batch writes. In this case, optimizing application logic is equally important. For databases, you can enable caching and batch commits. For example, in MySQL, you can change the innodb_flush_log_at_trx_commit parameter to 2 to reduce frequent disk writes. For logging systems, you can introduce a buffered write mechanism or use a centralized solution like Elastic Stack to centrally write logs to a separate storage server to reduce pressure on the primary SSD.

If the SSD write speed remains slow after completing the above adjustments, performance degradation may be due to drive aging or excessive write volume. At this point, you need to use a tool to monitor the SSD's health, such as the smartctl command:

sudo smartctl -a /dev/sda

Check the wear level and error rate. If the number of write-erase cycles is nearing its limit or a large number of bad blocks are present, consider replacing the SSD. For mission-critical South Korea CN2 servers, it's recommended to use enterprise-grade SSDs rather than consumer-grade SSDs. Enterprise-grade products typically offer higher endurance and performance, and include features like power-loss protection, effectively minimizing data loss from unexpected events.

In summary, methods for resolving slow SSD write speeds on South Korea CN2 servers include enabling and regularly performing TRIM, properly configuring the I/O scheduler to maintain sufficient free space on the disk, selecting an appropriate file system, adjusting kernel parameters, optimizing application write logic, and regularly monitoring SSD health.