Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Rich <rich@example.invalid>
Newsgroups: comp.os.linux.misc
Subject: Re: News : ARM Trying to Buy AmperComputing
Date: Wed, 22 Jan 2025 20:08:37 -0000 (UTC)
Organization: A noiseless patient Spider
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The Natural Philosopher <tnp@invalid.invalid> wrote:
> On 21/01/2025 19:56, Rich wrote:
>> For SSD's, writes occur to an "erased" flash block (typically much
>> larger than a "disk sector" size used by the host) and given enough
>> writes over a short enough timeframe the SSD controller can run out of
>> "pre-erased" blocks to use, and when that happens write speed slows
>> down to the rate that can be done when a "block erase" has to occur
>> before the actual writes can hit the media.  Note that this "block
>> erase" can also invove moving any partially used data sectors out of
>> the block into another block, creating a "write amplification"
>> situation as well.
> 
> One of the best ways to gain speed and longevity is to buy an SSD that 
> is way larger than you need. So it always has empty blocks available.

And hope it has a decent block layer that spreads the writes around so 
no one part of the flash is written to more than any other parts.

> And can do the block erases in background

Most SSD's do erases in the background, so that they can have empty 
blocks waiting to absorb writes.

But stream a large enough set of writes at the drive, and you can (for 
some drives) use up the queue of background erased blocks and then you 
see your write speed drop by a good amount because the block erases are 
now also part of the "write path" for your data heading at the drive.