ssd区块大小和扇区大小
SSDs seems to come in quite a variety of ‘new’ sizes these days, but why is that? Today’s SuperUser Q&A post has the answers to one curious reader’s question.
如今，固态硬盘似乎有各种各样的“新”尺寸，但是为什么呢？ 今天的“超级用户问答”帖子回答了一个好奇的读者的问题。
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.
今天的“问答”环节由SuperUser提供，它是Stack Exchange的一个分支，该社区是由社区驱动的Q＆A网站分组。
Photo courtesy of Jung-nam Nam (Flickr).
问题 (The Question)
SuperUser reader Dudemanword wants to know why SSDs seem to come in weird GB sizes:
超级用户阅读器Dudemanword想知道为什么SSD似乎具有怪异的GB大小：
Why do SSDs come in sizes like 240 GB or 120 GB rather than the normal 256 GB or 512 GB? Those numbers make much more sense than the 240 GB or 120 GB size.
为什么SSD的大小为240 GB或120 GB，而不是正常的256 GB或512 GB？ 这些数字比240 GB或120 GB大小有意义得多。
Why do companies manufacture SSDs in what seem to be “non-standard” sizes?
为什么公司要制造看起来“非标准”尺寸的SSD？
答案 (The Answer)
SuperUser contributors Patrick R. and Adam Davis have the answer for us. First up, Patrick R.:
超级用户贡献者Patrick R.和Adam Davis为我们提供了答案。 首先，Patrick R .：
While a lot of modern SSDs like the 840 EVO series do provide the sizes you are used to, like the mentioned 256 GB, manufacturers used to preserve a bit of storage for mechanisms fighting performance drops and defects.
虽然像840 EVO系列这样的许多现代SSD确实提供了您所习惯的大小，例如上述提到的256 GB，但制造商过去常常保留一些存储空间以应对性能下降和缺陷的机制。
If you, for example, bought a 120 GB drive, you can be pretty sure that it is really 128 GB internally. The preserved space simply gives the controller/firmware room for stuff like TRIM, Garbage Collection, and Wear Leveling. It was common practice to leave a bit of space unpartitioned – on top of the space that had already been made invisible by the controller – when SSDs first hit the market, but the algorithms have gotten significantly better, so you should not need to do that anymore.
例如，如果您购买了120 GB的驱动器，则可以确定它在内部确实是128 GB。 保留的空间只是为控制器/固件空间提供了诸如TRIM，垃圾回收和损耗均衡之类的空间。 当SSD首次投放市场时，通常的做法是在控制器已经变得不可见的空间之外保留一些未分配的空间，但是算法已经变得更好，因此您无需这样做不再。
EDIT: There have been some comments regarding the fact that this phenomenon has to be explained with the discrepancy between advertised space, stated in Gigabytes (i.e. 128 x 10^9 Bytes) versus the Gibibyte value the operating system shows, which is – most of the time – a power of two, calculating to 119.2 Gibibyte in this example.
编辑：关于这一现象的一些评论，必须用广告空间(以千兆字节(即128 x 10 ^ 9字节)表示)与操作系统显示的千兆字节值之间的差异来解释，即–时间-2的幂，在本示例中为119.2 Gibibyte。
As for as I know, this is something that comes on top of the things already explained above. While I certainly can not state which exact algorithms need most of that extra space, the calculation stays the same. The manufacturer assembles an SSD that indeed uses a power of two number of flash cells (or a combination of such), though the controller does not make all that space visible to the operating system. The space that is left is advertised as Gigabytes, netting you 111 Gibibyte in this example.
据我所知，这是上面已经解释过的事情的基础。 虽然我当然不能说明哪个确切的算法需要大部分额外空间，但计算结果保持不变。 制造商组装的SSD确实使用了两个闪存单元(或其组合)的电源，尽管该控制器并未使所有空间对操作系统可见。 剩下的空间被广告为GB，在此示例中为111 GB。
Followed by the answer from Adam Davis:
随后是亚当·戴维斯(Adam Davis)的回答：
Both mechanical and solid state hard drives have raw capacity greater than their rated capacity. The “extra” capacity is held aside to replace bad sectors, so the drives do not have to be perfect off the assembly line, and so that bad sectors can be re-mapped later during use with the spare sectors. During initial testing at the factory, any bad sectors are mapped to the spare sectors. As the drive is used, it monitors the sectors (using error correction routines) to detect bit level errors and when a sector starts going bad, it copies the sector to a spare, then re-maps it. Whenever that sector is requested, the drive goes to the new sector, rather than the original sector.
机械和固态硬盘驱动器的原始容量都大于其额定容量。 保留了“额外”容量来替换坏扇区，因此不必在生产线下完美安装驱动器，以便稍后可以在与备用扇区一起使用时重新映射坏扇区。 在工厂进行初始测试期间，任何坏扇区都将映射到备用扇区。 使用驱动器时，它将监视扇区(使用纠错例程)以检测位级错误，并且当扇区开始变坏时，它将扇区复制到备用磁盘，然后重新映射。 每当请求该扇区时，驱动器就会转到新扇区，而不是原始扇区。
On mechanical drives, they can add arbitrary amounts of spare storage since they control the servo, head, and platter encoding, so they can have a rated storage of 1 terabyte with an additional 1 gigabyte of spare space for sector re-mapping.
在机械驱动器上，由于它们控制伺服，磁头和磁盘的编码，因此它们可以添加任意数量的备用存储，因此它们的额定存储为1 TB，另外还有1 GB的备用空间用于扇区映射。
However, SSDs use flash memory, which is always manufactured in powers of two. The silicon required to decode an address is the same for an 8 bit address accessing 200 bytes as an 8 bit address accessing 256 bytes. Since that part of the silicon does not change in size, then the most efficient use of the silicon real estate is to use powers of two in the actual flash capacity.
但是，SSD使用闪存，闪存通常以2的幂进行制造。 对于访问200字节的8位地址和访问256字节的8位地址，解码地址所需的硅片相同。 由于那部分硅的尺寸不变，因此，最有效利用硅面积的方法是在实际闪存容量中使用2的幂。
So the drive manufacturers are stuck with a total raw capacity in powers of 2, but they still need to set aside a portion of the raw capacity for sector re-mapping. This leads to 256GB of raw capacity providing only 240GB of usable capacity, for instance.
因此，驱动器制造商的总原始容量为2的幂，但是他们仍然需要留出一部分原始容量用于重新映射扇区。 例如，这导致256GB的原始容量仅提供240GB的可用容量。
Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
有什么补充说明吗？ 在评论中听起来不错。 是否想从其他精通Stack Exchange的用户那里获得更多答案？ 在此处查看完整的讨论线程。
翻译自: https://www.howtogeek.com/188101/why-do-ssds-come-in-unusual-sizes/
ssd区块大小和扇区大小