Mailinglist Archive: opensuse (856 mails)

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Re: [opensuse] Reliable way to backup hard drive before clean install
On 10/05/2016 07:41 AM, Carlos E. R. wrote:

This is now normal practice with modern disk drives and is taken care of
by the
on-baord electronics so that the computer operating system sees an
unblemished
linear array of sectors no matter how they might be organized at the
physical level.

XFS is adding checksums for at least metadata sectors, and they are
considering data checksums, so that file integrity is guaranteed. Btrfs
I think is going a similar route, after all, they share several devs.

That is serving quite a different purpose.

The purpose of the drive's on-board electronics implementing sector look-aside
is to, as I said, present a 'clean disk' to the device drivers of the OS.

The file system sits above that.
Guaranteeing file integrity is about facing different problems.

part of the transition from V6 UNIX to V7 UNIX, for example, was to treat the
handling of the metadata of the file system differently, simple that the file
system of that time was. Writing the structural and the inode information
before the data information enabled FSCK to recover file system problems,
problems that HAD NOTHING WHAT TO TO WITH THE INTEGRITY OF THE PHYSICAL DISK
ITSELF.

In a more modern context, different file systems address this in a different
way, treating metadata and structural information different from content data,
each in their own way. Some permit the metadata to we written to a separate
device!

For the most part, this is not about the integrity of the physical disk, though
that might be a benefit in some ways, though given the ways a modern disk can
fail I doubt it.

It is about abuse. its for situations where the system crashes, perhaps a
power-out, perhaps a wiring fault or disconnect, so that a FSCK can do a
recovery. Or better still, the file system can recover itself without an
explicit FSCK.

Yes it is possible that a disk starts to fail.
Its possible that it develops more bad sectors than the are allowed by the
reserved look-aside allocation. it is possible that the disk ages or that the
atmospheric sealing fails and dust gets in and the error rate skyrockets.

Personally I don't think the kind of file system checks you describe or refer to
will be much use when that happens.

I say this because I have had that level of catastrophe happen and it basically
causes the disk to become unresponsive at a more fundamental level.

These integrity checks are good and useful, but they serve a different a
different purpose. Conflating the two purposes is not merely sloppy thinking
but will end up in wasted effort and perhaps even misguided application.

All of this is quite beside the point and has noting to do with the stated
object of a "Reliable way to backup hard drive before clean install".

We've offered many ways to do that and you keep bitching about errors in TARZ.
--
A: Yes.
> Q: Are you sure?
>> A: Because it reverses the logical flow of conversation.
>>> Q: Why is top posting frowned upon?

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