Re: Unable to mount hammer file system Undo failed

[Wojciech Puchar <wojtek@xxxxxxxxxxxxxxxxxxxxxxx>]

>> which i don't have at the moment.
>>
>
>
> just dd /dev/random and overwrite a few sectors?

good but... real failures are always worse than that.

In my tests ZFS for example (which for me is plain example of bad design 
and bad implementation) failed within less than hour to the point it was 
mountable but anything in /usr subdirectory was unreadable resulting in 
crash.

i willingly used machine with failed chipset, resulting in bad data in RAM 
every now and then. When it hit userspace it resulted in signal 11 or 
weird results of software.

After hitting kernel it resulted what i described.

i've wrote this HDD image for later tests. newer ZFS versions fixed crash, 
replacing it with message of error with still no data access.

memory corruption resulted in writing bad metadata, in all copies of 
course. ZFS is tree structured so the results was clear.

No offline fsck exist for ZFS because it is "not needed".

I actually agree. it is not needed, as well as ZFS ;)

As for me, what i really need is plain filesystem functionality.

I doesn't really need snapshots etc.

UFS is really fine for me, but seems like swapcache isn't well suited to 
cache it properly as Matthew Dillon said.

What i will need within a month is a service doing lots of I/O to some not 
that huge part of dataset, while keeping large files too.

swapcache is perfect fit for that workload if it would work.

All my "fears" aren't from nothing.
One should be picky about replacing something (UFS) that is close to 
perfect.

Thee fsck time is an overstated problem, over other problems.



On the same machine i was unable to destroy UFS after whole day of trying.
Of course it crashed. Of course it produced SMALL data loss (few files), 
fsck_ffs always fixed things properly.

This was under FreeBSD but DragonFly UFS is no different.


I really appreciate LOTS OF HARD WORK Of Matthew Dillon and others, but 
simply dismissing trusted UFS with over 20 years of history by stating 
"just use hammer" isn't good IMHO.