Re: reiser4 plugins

David Masover
2005-06-27T15:33:51Z

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Theodore Ts'o wrote:
> On Mon, Jun 27, 2005 at 12:21:38PM +0300, Markus T?rnqvist wrote:
>
>>On Thu, Jun 23, 2005 at 11:34:50PM -0400, Horst von Brand wrote:
>>
>>>David Masover <ninja@slaphack.com> wrote:
>>
>>>>I think Hans (or someone) decided that when hardware stops working, it's
>>>>not the job of the FS to compensate, it's the job of lower layers, or
>>>>better, the job of the admin to replace the disk and restore from
>>>>backups.
>>>
>>>Handling other people's data this way is just reckless irresponsibility.
>>>Sure, you can get high performance if you just forego some of your basic
>>>responsibilities.
>>
>>Your honest-to-bog opinion is that the FS vendor is responsible for
>>the admin not taking backups or the hardware vendor shipping crap?
>>
>>*still trying to understand how that can be*
>
>
> Most Linux users are using PC-class hardware. And Ted's First Law of
> PC-Class Hardware is: "Most of it is crap". And then there's Ted's
> Second Law, "Too many system administrators don't do backups".

Not our problem anymore. This is like saying that we should run all
filesystems in synchronous mode because some users will grab stuff out
of the computer without unmounting it -- even more a problem now that we
have SATA, which supports hot-swapping.

Too many system administrators don't do backups? Some day the building
will burn down and they will wish they had.

> So it's a matter of matching the filesystem to the needs of the user.

My needs are a filesystem which doesn't assume I'm an idiot who can't
make backups.

> If you have a filesystem which is blazingly fast, but which at the
> slightest sign of trouble, trashes your data, versus one which is fast
> but perhaps not-so-fast as the other filesystem, but which is much
> more reliable, which would you choose?

Hypothetically? I choose the faster one. Failures happen only rarely,
and when they happen, there's no telling how small or large they will
be, therefore I keep regular backups, and as soon as I see my hardware
starts to fail, I grab what I can off of it, merge that with the latest
backup, and buy new hardware.

> XFS has similar issues where it assumes that hardware has powerfail
> interrupts, and that the OS can use said powerfail interrupt to stop
> DMA's in its tracks on an power failure, so that you don't have
> garbage written to key filesystem data structures when the memory
> starts suffering from the dropping voltage on the power bus faster
> than the DMA engine or the disk drives. So XFS is a great filesystem
> --- but you'd better be running it on a UPS, or on a system which has
> power fail interrupts and an OS that knows what to do.

XFS, Reiser3, and Reiser4 all pass the pull-the-plug test. Maybe I just
haven't pushed them hard enough?

> Ext3, because
> it does physical block journalling, does not suffer from this problem.
> (Yes, Resierfs uses logical journalling as well, so it suffers from
> the same problem.)

I don't actually understand the difference here. Are we talking about
metadata journalling vs. data journalling?

> So perhaps it's not the job of the FS vendor to be responsible for
> crap hardware or lazy sysadmins that don't do backups.

Good! Glad we agree!

> But a system
> administrator who knows that he doesn't do backups frequently enough,
> or is running on cheap, crap hardware, would be wise to consider
> carefully which filesystem he/she wants to use given the systems
> configuration and his backup habits.

Given a choice between changing filesystems or getting a Streamload
account, I choose Streamload. (streamload.com)

Given a choice between reformatting or editing cron, I'd edit cron.

> Me, I'll go for the robust filesystem, just on general principles. As
> a friend from the large-scale enterprise storage world once put it,
> "Performance is Job 2. Robustness is Job #1." (Of course, if you
> want to put your fragile filesystem on a multi-million dollar
> enterprise storage system such as an IBM Shark or an EMC Symmetrix
> box, I'm sure IBM or EMC will be happy to sell you one. :-)

Job 1 is done by either that system or by good backups. Don't overkill
Job 1 at the expense of Job 2.
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