Re: ZFS with Linux: An Open Plea

Tomasz Kłoczko
2007-04-16T15:27:54Z

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On Mon, 16 Apr 2007, Adrian Bunk wrote:

> On Mon, Apr 16, 2007 at 04:01:23PM +0200, Tomasz Kłoczko wrote:
>> ...
>> Few days ago I'm swich two backup servers with few TB storage from Linux to
>> Solaris .. only because client want use ZFS .. because ZFS is EXCELENT for
>> this kind tasks (only because it allow save many thousands of
>> <put_your_currency_name> because it allow better utilize the same storage)
>> and trust me .. cases like this will be more .. much more and changing
>> licensing Linux code will be MUCH more easier than reinventing wheel (wich
>> will be reimplemnting ZFS under GPL).
>
> This is a technical mailing list, so let's start with technical
> arguments:
>
> Why did this client want to use ZFS?

Because switching to Solaris was chipper than buying next faster FC/SCSI
storage. Simple ?

> Because his boss was convinced by a marketing guy that ZFS was the best
> invention since sliced bread?

In this scenario ther is no place for "marketing guy" .. try again ..
(maybe it can occure in US or Germany but trust me .. not in Poland 8-)

> Or due to technical limitations in what Linux currently offers
> resulting in ZFS bringing him direct advantages on these servers?

Yes .. it is Linux limitiations because it is very hard to provide
simultanouse streams of backup data with threaded compression (using in
this case pbzip2) with good CPUs utilization because most streams waits on
I/Os and most of CPUs are not fully utilized. All this becase single stram
of compressed data can't be easy dinamically switched to another (not
busy) disk in JBOD. ZFS by two level allocation (on device and block
level) will not wait for finish I/O but will try use another/not busy
device in ZFS pool. This is *main* reason integrate in one layer VFS and
LVM in case ZFS. By integrate this two layers you can make deciion where
data will be written depending on *current* devices utilization. In all
other "classic" ways you will break layered OS model .. so in ZFS case
conclution like "we must integrate this two layers in one" it is not bug
but feacture and was FUNDAMENTAL.

This is not all .. backup data must be safe in best possible form .. in
time .. and it mean in this case that checksumming is NECCESSARY. Look ..
ext4 for now only have plans for implemting checksuming
(http://www.bullopensource.org/ext4/files/ext4.txt) and ATM on Linux there
is no FS with this kind abilities .. so yes again: this was Linux
technical limitation.

>> Problem is not on technical area but on licensing and it is plain Linux
>> word problem because neccessary in this case changes on CDDL side will make
>> this code less oppended than now .. so you can (probably ?) forget about
>> GPLing ZFS code (and ZFS it is not all what will good to have from Sol in
>> Linux).
>> IMO current Linux licensing less is importand than bringing in possible
>> simpler way things like ZFS to Linux. So best/simpler way will be start
>> change Linux licensing for save all GPL goodies and allow interract with
>> code on license like CDDL.
>>
>> Licensing is for allow keep in best possible form Linux. If it can't do
>> this in best possible way it must be change (must evolve .. like many othes
>> things around).
>
> There are at about 10.000 people who contributed to the Linux kernel,
> some of them unreachable or even dead.

Do you know who was Paracelsus ? He was medic hundriet years ago. They
discover and verbalise some kind fundamental (?) law for medicine which
can be used not only on medicine area. He sayd "kills not subtance but
dose of substance". So anything can kill you/animal/project .. you can
kill someon also using oxigen (not only low level of oxigen kills but also
to much can kill). Try to think on how this law on how many diffret ways
can be trasformed/appied to this kind of arguments. Look on how many
developers migrate to another unices in last few years (count only two for
simplicity like Solaris and MOX). Try looking for public forums statistics
for example Linux vs. Solaris and after this try to answer on "is it 10k
is it realy big number in this case or not ?" (IIRC google provides very
good tools for anyone who want this kind answers).

kloczek
--
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*Ludzie nie mają problemów, tylko sobie sami je stwarzają*
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Tomasz Kłoczko, sys adm @zie.pg.gda.pl|*e-mail: kloczek@rudy.mif.pg.gda.pl*