Re: [gentoo-user] Re: USB crucial file recovery

[J. Roeleveld]

On Thursday, September 01, 2016 08:41:39 AM Michael Mol wrote:
> On Wednesday, August 31, 2016 11:45:15 PM Alan McKinnon wrote:
> > On 31/08/2016 17:25, Grant wrote:
> > >> Which NTFS system are you using?
> > >>
> > >> ntfs kernel module? It's quite dodgy and unsafe with writes
> > >> ntfs-ng on fuse? I find that one quite solid
> > >
> > > I'm using ntfs-ng as opposed to the kernel option(s).
> >
> > I'm offering 10 to 1 odds that your problems came from ... one that you
> > yanked too soon
>
> (pardon the in-line snip, while I get on my soap box)
>
> The likelihood of this happening can be greatly reduced by setting
> vm.dirty_bytes to something like 2097125 and vm.dirty_background_bytes to
> something like 1048576. This prevents the kernel from queuing up as much
> data for sending to disk. The application doing the copy or write will
> normally report "complete" long before writes to slow media are
> actually...complete. Setting vm.dirty_bytes to something low prevents the
> kernel's backlog of data from getting so long.
>
> vm.dirty_bytes has another, closely-related setting, vm.dirty_bytes_ratio.
> vm.dirty_bytes_ratio is a percentage of RAM that is used for dirty bytes. If
> vm.dirty_bytes_ratio is set, vm.dirty_bytes will read 0. If vm.dirty_bytes
> is set, vm.dirty_bytes_ratio will read 0.
>
> The default is for vm.dirty_bytes_ratio to be 20, which means up to 20% of
> your memory can find itself used as a write buffer for data on its way to a
> filesystem. On a system with only 2GiB of RAM, that's 409MiB of data that
> the kernel may still be waiting to push through the filesystem layer! If
> you're writing to, say, a class 10 SDHC card, the data may not be at rest
> for another 40s after the application reports the copy operation is
> complete!
>
> If you've got a system with 8GiB of memory, multiply all that by four.
>
> The defaults for vm.dirty_bytes and vm.dirty_background_bytes are, IMO,
> badly broken and an insidious source of problems for both regular Linux
> users and system administrators.

I would prefer to be able to have different settings per disk.
Swappable drives like USB, I would put small numbers.
But for built-in drives, I'd prefer to keep default values or tuned to the 
actual drive.

--
Joost