Optimizing SSD Operation for Linux

Transcription

1 ACTINEON, INC. Optimizing SSD Operation for Linux 1.00 Davidson Hom 3/27/2013 This document contains recommendations to configure SSDs for reliable operation and extend write lifetime in the Linux environment.

2 Date Revision Author Change 03/27/ DH Initial creation [1]

3 Contents 1 Overview Setup Journaling TRIM Logging of read access I/O Scheduler Temp and logs Browser caches Write-back caching Usage File I/O Overprovisioning Maintenance Write lifetime endurance Summary... 2 [i]

4 1 Overview SSDs have matured in recent years enough to become a mainstream product replacement for traditional rotating disks. Advantages such as resistance to shock and vibration, long MTBF, and faster data rates contribute to its increasing popularity. However, to ensure high performance, reliability and long lifetimes, it is critical the system is configured for correct SSD operation. 2 Setup 2.1 Journaling A journaling file system records a log of changes to the file system before committing the changes. In the event of a catastrophic failure (sudden power loss), files are less likely to get corrupted. Disabling journaling enhances the write lifetime endurance of SSDs by reducing the number of writes. It is debatable to leave journaling on or to disable it. 2.2 TRIM TRIM support lets an operating system tell an SSD when blocks are not in use and can be overwritten. If TRIM is supported, it functions to reduce write amplification, where a physical memory block is written multiple times. Ext4 file systems support TRIM. In order to function, both the file system and the SSD must support TRIM. 2.3 Logging of read access The noatime option in Linux prevents the logging of read accesses to the file system. Using this option will enhance the write lifetime endurance by significantly reducing the number of writes. 2.4 I/O Scheduler Changing the default I/O scheduler to NOOP, a minimal FIFO scheduler puts the task of disk scheduling away from the operating system and onto the SSD. SSDs do their own scheduling and do not require the operating system to decide where data should physically reside on the disk. 2.5 Temp and logs Moving /tmp /var/tmp and /var/log to a ram disk will reduce the number of writes to disk. 2.6 Browser caches Disabling browser caches or pointing them to /tmp will reduce the number of writes to disk. 2.7 Write-back caching Enabling write-back caching instead of write-through caching increases latency and reduces the number of writes to disk. [1]

5 3 Usage 3.1 File I/O Optimizing file I/O helps reduce the number of writes to memory cells. Application developers should implement file I/O block sizes to match that of the allocation unit size of the partition. 3.2 Overprovisioning Overprovisioning is a technique to increase write endurance and sustained performance on SSDs. Leaving additional free space, about 20-40% user capacity will aid in the internal garbage collection by allocating additional memory cells for scratchpad use. 4 Maintenance 4.1 Write lifetime endurance SSDs have limited write lifetime endurance, which is dependent on the workload. On an SSD with 4kB sized memory cells, 128KB sequential write endurance would be 40 times that of 4KB random write endurance. Monitoring media wearout or timed media workload wear information will aid in predicting the write lifetime endurance. At a minimum, an amount of data equal to double the size of the SSD must be written before monitoring. 5 Summary Special consideration is necessary when choosing to use an SSD in a Linux system. Reducing the number of writes to the SSD will significantly improve the write lifetime endurance and enhance performance. Thoroughly analyze the write characteristics of the SSD by measuring write wearout in the field to calculate realistic estimated write lifetime endurance. Choosing a high quality SSD is also critical in reducing issues with poor performance and lifetime endurance. Poor quality SSDs can have huge write amplification factors, which writes multiple times on the memory for each physical write. This decreases the endurance because of the multiple writes, as well as consuming bandwidth. Improved performance, reliability and write lifetime endurance can be achieved with proper attention to systems designed with SSD drives. [2]