Mailinglist Archive: opensuse (686 mails)

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Re: [opensuse] SSD and smartctl: Percentage Used Endurance Indicator: 34 ?
  • From: "Carlos E. R." <robin.listas@xxxxxxxxxxxxxx>
  • Date: Mon, 8 Jul 2013 19:08:55 +0200 (CEST)
  • Message-id: <alpine.LNX.2.00.1307081859540.6576@Telcontar.valinor>
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On Monday, 2013-07-08 at 11:25 -0400, Greg Freemyer wrote:

On Sun, Jul 7, 2013 at 1:42 PM, Carlos E. R. <> wrote:


However... you can not write, say, 100 bytes on flash media, you have to
write the entire 32KiB block. That is, read it, modify the 100 bytes you
need (in memory) and then write again the 32 KiB block. That makes for a
much larger figure.

Carlos,

I don't know where your 32 KiB block came from. Seems too big to be a
page and too small to be a erase block.

- From here:

<https://wiki.linaro.org/WorkingGroups/KernelArchived/Projects/FlashCardSurvey?action=show&redirect=WorkingGroups%2FKernel%2FProjects%2FFlashCardSurvey>
Flash memory card design

+++··························
FAT optimization

Most portable flash media come preformatted as with a FAT32 file system. This is not only done because there is support for this file system in all operating systems, it is actually a reasonably good choice for the media: The data on a FAT32 file system is always written in clusters of e.g. 32 KB, and the media are normally formatted with a cluster size matching the optimum write size, as well as aligning the clusters to the start of internal units, and the access patterns on a FAT32 file system are relatively predictable, alternating between data blocks, file allocation table (FAT) and directories.
··························++-

If you go further down the article, to the "List of flash memory cards and their characteristics", you see several of them have a write size of 32K, some 64K, even 256K. Few have less than 32K. In the list there is a section for SSD, and the write sizes are similar.


>> From a physical perspective you have to write an entire erase block
(EB) at time. EBs these days are often 2MiB or even bigger and even 3
or 4 years ago were 128KiB or bigger.

In 10 year old flash designs that meant to modify anything EB size or
smaller you did a read/modify/write (RMW) cycle of an entire EB. I
suspect that is what you are describing.

You need to give the SSD devs some credit, they realized that was a
stupid design a long time ago.
...
...

Ok, what I understand from what you post is that the firmware is clever and does what is needed internally, but it does in fact write a big block at a time to the flash memory.

- -- Cheers,
Carlos E. R.
(from 12.3 x86_64 "Dartmouth" at Telcontar)
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