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Western digital ssd health check4/11/2023 ![]() ![]() However, in some cases a higher-endurance SSD can provide higher write performance than a lower endurance SSD. TBW(1TB) = 1TB * 1 DWPD * 365 Days/Year * 5 Years = 1,825 TBW What Happens When You Get SSD Endurance WrongĬhoosing too high of an endurance SSD can often increase the initial cost. Take the case of a 15TB, “1 DWPD” SSD and a 1TB, “1 DWPD” SSD, both with a 5-year warranty. When SSDs have different capacities, the total amount of data you can write to them can vary dramatically. TBW to DWPD: DWPD = TBW / (365 * Warranty(Years) * Capacity(TB) ) “1 DWPD” Doesn’t Equal “1 DWPD”Ī common trap that users fall into when looking at SSD datasheets is assuming that “1 DWPD” on one drive means the same as “1 DWPD” on another drive. Alternatively, if a 1TB SSD is specified for 10 DWPD, it can withstand 10TB of data written to it every day for the warranty period.Īnother metric used for SSD write endurance is Terabytes Written (TBW), which describes how much data can be written to the SSD over the life of the drive.Ĭonverting between TBW and DWPD is simple:ĭWPD to TBW: TBW = Capacity(TB) * DWPD * 365 * Warranty(Years) In other words, if a 1TB SSD is specified for 1 DWPD, it can withstand 1TB of data written to it every day for the warranty period. SSD endurance is commonly described in terms of Drive Writes Per Day (DWPD) for a certain warranty period (typically 3 or 5 years). The more experience a company has with end-user workloads and the flash, itself, (SanDisk, a Western Digital brand, has over thirty years history in this!) the more intelligence it can embed in this firmware to help maximize endurance. This additional flash is not visible to the user, but it is visible to the drive and used to enhance endurance by allowing for more efficient data management.įinally, the program that runs in the SSD, the firmware, can intelligently manage the flash inside of the SSD. Overprovisioning adds additional flash capacity to the SSD. Western Digital improves SSD endurance with three main technologies: error correction, overprovisioning, and firmware.Īdvanced error correction techniques such as HGST’s CellCare™ NAND management technology or SanDisk®’s Guardian Technology™ can help retrieve data from even marginal flash cells and can dramatically extend the NAND cell’s usable lifetime. Technology placed around the NAND by the manufacturer can change endurance as well, for better or worse. Thankfully, SSD endurance isn’t set by P/E cycle limits alone. Error Correction, Overprovisioning, and Firmware This decrease in cycles is obviously a bad thing for endurance. As the industry transitions from Multi Level Cell (MLC) to Triple Level Cell (TLC) SSDs, which store 3 bits per cell, the available P/E cycles decrease. These cycles occur whenever existing data needs to be overwritten in a flash cell. SSD endurance is limited because the NAND flash that powers SSDs has a finite number of “program/erase” (P/E) cycles before it can’t be used anymore. The physics of SSD endurance are complicated, but the results are simple: SSDs wear out as you write to them. Choose the wrong SSD endurance and you’ll end up replacing the drive early or overpaying for a higher endurance drive than needed. ![]() SSD endurance is the total amount of data that an SSD is guaranteed to be able to write under warranty, often specified in “TBW” or “DWPD” (which we’ll discuss a little later). There’s one more choice you need to make, and it’s a choice you might not have had to make before: the SSD endurance level. You also need to choose the right capacity, of course, anywhere from 100s of gigabytes to multiple-terabytes. You need to select from three major, incompatible interfaces ( SATA, SAS, or NVMe™). ![]() You have to pick the right the form factor so that the drive will fit in your server. Choosing the right SSD is a complicated process, after all. You’ve probably looked at an SSD datasheet and been a little overwhelmed. In this post I’ll discuss SSD endurance and how this affects your choice of SSD, plus give you some rules of thumb for making the right choice. ![]() My first post discussed the role of latency in storage architectures. This is my second post in the “Speeds, Feeds, and Needs” blog series, designed to explain the more technical elements of enterprise storage in terms that are understandable to everyone. ![]()
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