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我所知道的关于 SSD 的一切
Everything I Know About SSDs
2020 — 2024，它一次次回到首页
黑点是上首页（≥ 50 分）的那次投稿，空心点是没冲上去的投稿，点越大分数越高。
导读
这是一篇关于 SSD（固态硬盘）工作原理的科普长文，涵盖 NAND 闪存特性、磨损、TRIM、文件系统与 SSD 的交互等知识。文章多次登上 Hacker News 首页，被视为 SSD 入门的经典参考资料。
为什么经久不衰：SSD 的底层机制（闪存写入方式、TRIM、磨损均衡）至今仍是许多开发者容易误解的领域，这篇系统性的讲解历经多年仍被反复推荐。
HN 评论精选
指出原文关于文件系统和 HDD 扇区的两处技术性错误
文中关于文件系统的部分略有不准。'文件系统的处理方式与 NAND 闪存的工作机制不兼容'——这对大多数传统文件系统成立，但日志结构文件系统对闪存友好得多，这也是它们重新受到关注的原因，典型的闪存转换层（FTL）就与日志结构文件系统惊人地相似。此外还有闪存专用文件系统。'对 HDD 来说所有扇区都一样'也不对，因为有坏块重映射机制；而且让磁盘知道哪些块未使用也很有用，可以不实际读介质就返回全零。TRIM/discard 在涉及 RAID 和虚拟块设备时会相当复杂。
notacoward查看英文原文
The part about filesystems is slightly incorrect. > The way the file system handles this is incompatible with the workings of NAND flash. That's true of most conventional filesystems, but log-structured filesystems are much more flash-friendly. That's why there has been a resurgence of interest in them, and also why a typical flash translation layer bears a striking resemblance to a log-structured FS. There are also flash-specific filesystems. > to an HDD all sectors are the same. This is not true because of bad blocks. Every disk has a reserve of blocks that can be remapped in place of a detected bad block, transparently, much like flash blocks are remapped. Beyond that, it's also useful for a disk to know which blocks are not in use so it can return all zeroes without actually hitting the media. There are special flags to force media access and commands to physically zero a block, for the cases where those are needed, but often they're not. Trim/discard actually gets pretty complicated, especially when things like RAID and virtual block devices are involved.
来自运维一线的 SSD 实战经验：固件风险、厂商差异与使用建议
我在 prgmr 使用 SSD 学到的：SSD 固件比硬盘复杂得多，更可能直接彻底变砖而非优雅降级，厂商还可能有恶劣的固件 bug（如 HPE SSD 在使用 32768 小时后失效的 bug）。建议在 RAID 中混用不同寿命和不同厂商的 SSD。各厂商在负载下跑 SMART 测试的行为差异很大；不同 SSD 对电源波动的容忍度也不同；无法使用 TRIM 时手动超额配置很有帮助；secure-erase-enhanced 的具体行为各盘也不一样。
sn查看英文原文
Things I've learned from using SSDs at prgmr: Since the firmware is more complicated than hard drives, they are way more likely to brick themselves completely instead of a graceful degradation. Manufacturers can also have nasty firmware bugs like https://www.techpowerup.com/261560/hp-enterprise-ssd-firmware-bug-causes-them-to-fail-at-32-768-hours-of-use-fix-released . I'd recommend using a mix of SSDs at different lifetimes, and/or different manufacturers, in a RAID configuration. How different manufacturers deal with running SMART tests under load drastically varies. Samsung tests always take the same amount of time. The length of Intel tests vary depending on load. Micron SMART tests get stuck if they are under constant load. Seagate SMART tests appear to report being at 90% done or complete, but the tests do actually run. Different SSDs also are more or less tolerant to power changes. Micron SSDs are prone to resetting when a hard disk is inserted in the same backplane power domain, and we have to isolate them accordingly. Manual overprovisioning is helpful when you aren't able to use TRIM. What a drive does with secure-erase-enhanced can be different too. Some drives only change the encryption key and then return garbage on read. Some additionally wipe the block mappings so that reads return 0.
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