[TUHS] The evolution of Unix facilities and architecture

Toby Thain toby at telegraphics.com.au
Fri May 12 11:05:55 AEST 2017


On 2017-05-11 7:47 PM, Dave Horsfall wrote:
> On Thu, 11 May 2017, Larry McVoy wrote:
>
> [...]
>
>> Try the same thing with Linux.  The file system will come back, starting
>> with, I believe, ext2.
>
> That's a journalled FS, isn't it?  In which case the transactions get
> replayed.

No, I think ext3fs was the first version that was journaled.

So was reiserfs. With pull-plug tests I could get ext3fs to toss cookies 
but not reiserfs.

Now of course the state of the art is copy-on-write, like ZFS.

--Toby


>
>> My belief is that Linux orders writes such that while you may lose data
>> (as in, a process created a file, the OS said it was OK, but that file
>> will not be in the file system after a crash), but the rest of the file
>> system will be consistent.  I think it's as if you powered off the
>> machine a few seconds earlier than you actually did, some stuff is in
>> flight and until they can write stuff out in the proper order you may
>> lose data on a hard reset.
>
> And FreeBSD (at least) has been doing ordered writes for quite some time.
>



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