I am reading up on solid state devices. I understand that if you format a USB flash drive, it wears the cels on the device. However, for sanitation purposes, what I do is overwrite with 0's anyway.

I read somewhere, that the controller for the device does maintenance to keep the drive alive. So there is no guarantee that a cel is cleared.
I'm not sure I have a good understanding of this, so let me ask a question about this.

If I look at the drive size with fdisk and 0 the drive to that many bytes, then check the drive for 0's and it clears. It means the controller did overwrite all the cels. Or is that something else?

The explanation said that some cels that fail are not used.

Does this also mean that if I check the disk size later, it will be smaller? or will it have badblocks?

I would like a clear understanding of this, so please if you can, go into detail about this for me.

Thank you.

SSD's (Solid State Drives) and more traditional "mechanical" drives work in a different way because there are diffrent technologies involved. The more traditional "mechanical" drive has a spinning platter (where the data itself is stored) with a read/write head that spins to witch ever part of the platter has the data, that's being requested by the system.

SSD drives have chips that hold the data instead of a spinning platter. Data on SSD drives never gets overwritten, a certain number of file system blocks get reserved for when new data is written, with the old blocks then being 'marked' to be erased at some future point in time.

Only if you filled the WHOLE drive with zeroes would you stand any chance of data being overwritten, and even then the controller might swap some of the reserved cells in and out so some might be missed.
Writes are accomplished by first issuing a delete and then a write. The controller will mark data you delete as deleted and will wait for a quiet time to actually delete them unless a write is issued by the controller to that cell.
Also SSDs will rearrange data to make access more efficient- called housekeeping- if left powered up while the system is idle.

David, SSD drives do NOT overwrite data, the blocks must be erased first, BEFORE any data can be written to it. Zero'ing an SSD drive is the worst (or close to it) thing you could do!

Why don't you read posts before you make such comments???
You even quote what I said, but still did not read it.
To REPEAT: "Writes are accomplished by first issuing a delete and then a write."
At no time did I suggest that writing zeroes to it was a good idea. In fact I implied that it would not achieve the desired result.

deleted

Hi,

I would suggest to look at https://en.wikipedia.org/wiki/Solid-state_drive and SSD memory cell clearing wikis to get some help in understanding functions for SSD devices; You can dig deeper into the above mentioned wiki pages to gain better understanding.

Hope this helps.
Have fun & enjoy!

What I understand is that when a SSD is filled to almost its maximum, writes are performed at the same cells over and over. So if you have 100 MB of free space and you write/replace 50 MB every day, cells are being written every two days. If the cells lifetime is 200 write cycles, the average failure occurs in 400 days. Average, which means that failure can occur much sooner.

If, OTOH you have 4 GB of free space on that drive, the same cells are only written every 80 days. So it takes much longer before 200 write cycles are reached for all cells.

This is not in contradiction with OneBuck's quotes. Just my rule to increase reliability on SSD drives. Make sure you have plenty of free space.

jlinkels

jlinkels

I think you will find that the housekeeping done by the controller will move data around to ensure that those frequently written cells are moved around the drive to ensure wear levelling.

Errr... yes, but does that improve anything? If I have a 4GB SSD and 3.9 GB of static data? Either the wear leveling algorithm does nothing and my statement holds. Or the wear leveling algorithm moves around 50 MB or 100 MB and does another write operation into that free space. The only difference is that it is static data written into that space instead of my dynamic data.

jlinkels

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Most of my usb drives have been good until I do something IO intensive on them. Like compiling sources. Or downloading torrents. I've used most of them as my primary linux install > 6 months. The ones I do IO stuff on seem to last half that time or less. I've only had one fail so far, but I do have trust issues. Avoid getting them > 50% full and you can avoid a lot of issues.

Yes but static data is updated less often and it is also revisited and reorganised dynamically. Data is also re-arranged so that often changed small files are placed together in the same 4k block wherever possible and will therefore be more likely to remain in buffers and not need rewriting as often.

SSDs parallelize reads and writes. Flash chips are actually slower than metal platters. But SSDs write to many different chips at once. By the time the first chip is done with the write, the controller is issuing another write to it.

Because of the almost random nature of writing a SSD, even if you try to fill it up with zeroes, it probably won't be full. But every SSD manufacturer makes an erase utility for their drives. That's what should be used. But if the information is of great importance, the drive should physically shredded. A blender works well for SSDs, and smart phones too.

USB flash drives also parallelize writes, but the firmware is etched in the controller. It's not very sophisticated. Some of the operating software actually exists on the drive. If you take a 30MB/s drive, write zeroes to the first MB or two several times, and then reformat it, it will be a 3MB/s drive after that.