[TUHS] If not Linux, then what?

Arthur Krewat krewat at kilonet.net
Tue Aug 27 10:59:02 AEST 2019

On 8/26/2019 8:30 PM, Larry McVoy wrote:
> I really don't understand the love for ZFS.  I hired Bonwick and I
> hired Moore, I had high expectations but they were all dashed when I
> realized ZFS doesn't use the page cache.  That's so crazy busted I lost
> all interest in ZFS.  ZFS took us back to HP-UX mmap semantics.

At the risk of going off-topic:

 From a system-administration standpoint, and data-integrity standpoint, 
ZFS was a huge step forward. In my humble opinion ;)

Besides the obvious (to me) benefits of adding mount points, adjusting 
volume sizes, and all the other things that ZFS does, I have yet to find 
any mainstream filesystem (if you can call ZFS "just" a filesystem) that 
guarantees data integrity. I have an office server, that contains a lot 
of source code and archived data that I depend on religiously. I do 
copious backups to LTO tapes as well as an off-site Amazon EC2 instance.

Within the recent past few years, I had an issue with a Dell MD Raid 
array where ZFS was complaining about checksum errors on a certain disk. 
Data was being corrupted on the fly. It seems that the writes were being 
corrupted, not reads. Thankfully, it was on a RAIDZ2 volume, where it 
could correct the corruption. The corruption in question was on files 
that are dated back to the early 90's.

Stopping bit-rot in it's tracks, ZFS has done me well.

As for what mmap() doesn't do right, I started using memory mapped files 
back in the early 80s on VMS on a VAX-11/780 when I and a colleague were 
converting a database from TOPS-10 to VMS. Perhaps I am misunderstanding 
your dislike for mmap() but please, enlighten me. It was my 
understanding at the time that it was akin to swapping/virtual-memory 
using an MMU. The difference was that instead of using the main paging 
area, the kernel would use an actual file.  Why would mmap() be a bad 
thing, when it's hooked into the kernel, and possibly hardware, at such 
a low point?

art k.

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