Linux @lemmy.ml swizzle9144 @lemmy.blahaj.zone 1 yr. ago

Confused about the Write Zeroes command

I'm shopping for a new NVMe SSD drive for my laptop and with the second deciding factor being Linux compatibility, I'd looked up the names of specific drives in the source code of Linux and discovered that their controllers have quirks that have to be worked around.

Now, I figured out more or less how quirks affecting one of the controllers impact its functionality under Linux, but there's another controller that I have a trouble understanding how disabling the aforementioned command limits the functionality of, if at all; therefore I'd like to ask you all, under what circumstances is the command used by a host and can disabling it lower the performance or power efficiency of an impacted controller/drive?

To be clear, the quirk workaround I'm talking a about is NVME_QUIRK_DISABLE_WRITE_ZEROES.

22 comments

Considering what specific nvme drive to use on Linux hasn't been a real problem for at least 5 years, especially if you just plan to stick it in a laptop. Just buy a drive from a reputable brand from a reputable source.
I have a WD black SN770 in my main desktop and it works no issues. I even have btrfs on it, and some people suggested that btrfs would have some issues with nvmes, but here I am over a year later with zero issues. Speed on these things is out of this world.
- That's good news, but what if this affects wear leveling? Or efficiency in some other way, that would result in these dying sooner than expected (still years probably, but.. yeah)
  
  I make back ups. If this dies, I'll get another one. They became very cheap lately. 1TB is like $55
- What were the reported problems of BTRFS on an NVME? There are actually a few upsides to BTRFS on flash: if you enable compression there will be less writing to the flash, and reflinking capabilities means that copy-pastes to the same partition won't cause extra writes.
  
  I've heard about freezing. Screens going black and so on. Never had any of those issues
I am coming at this from a more general angle, so this may not be as applicable.

When a repeated series of inputs is written to a drive, a number of optimisations can be applied. If the user wants a large number of zeros written, the drive's firmware can use a short cut. Instead of writing those zeros, it can make a note that a number of blocks, at a location, are all zero.

This becomes apparent if one runs fio against the raw block devices versus a software later like LVM. Some operations against some layers will be unreasonably fast. There is a lot of nuance to this.

My read of the quirk is an incompatibility between what Linux expects and the firmware. Enable the quirk only if the dmesg errors are present. Do not expect that the drive has been zeroed. If you want your data secure at disposal of the drive, the then use encryption.
- Thanks a lot! This clarifies it for me, and if I understand correctly, it shouldn't be a concern for me since my laptop isn't used for data-intensive computing.
- What if you try to wipe a NVME-drive for which this quirk is enabled by default in the kernel? Does that mean that even if you used something like the 'erase device' function in GNOME Disks on said drive, it would in fact not actually completely zero the drive? What if you use GNOME Disks to wipe a partition on said drive?
  
  Or does this quirk refer to an entirely different operation?
  
  A bit outside of my knowledge, but I understand that too be a long standing issue. Wiping issues are a good reason to encrypt a NVMe drive.
  
  This page suggest the nvmi-cli has a secure format command that will do it. http://blog.pythonaro.com/2018/05/how-to-securely-wipe-nvme-drive.html?m=1
  
  Hopefully, someone more knowledgeable will also tag me in their response.
Isn't that referring to the write zeros ata command to erase the whole drive?
- No, it is referring to the NVMe write zeroes command that is used to set a range of blocks to zero. It seems like it is related to deallocate/TRIM functionality but I can only find documentation about the command without a good definition of why it would be used.
  
  Some drives say they support it but don’t really, or it negatively affects performance, so they have quirks.
  
  What if you try to wipe a NVME-drive for which this quirk is enabled by default in the kernel? Does that mean that even if you used something like the 'erase device' function in GNOME Disks on said drive, it would in fact not actually completely zero the drive? What if you use GNOME Disks to wipe a partition on said drive?
  
  Or does this quirk refer to an entirely different operation?

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