Re: ZFS with Linux: An Open Plea

Tomasz Kłoczko
2007-04-16T20:18:48Z

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On Mon, 16 Apr 2007, Diego Calleja wrote:

> El Mon, 16 Apr 2007 17:46:50 +0200 (CEST), Tomasz Kłoczko <kloczek@rudy.mif.pg.gda.pl> escribió:
>
>> also some other interestig numbers can be founnd on:
>> http://milek.blogspot.com/2006/08/hw-raid-vs-zfs-software-raid-part-ii.html
>
> So software raid can be faster than HW raid. News at 11.

Of cources it can be true in most cases (probably for some more advanced
RAID controlers). Few weeks ago I perform some basic test on Dell 2950
with 8x73GB SAS disk .. just as for kill time (waiting for access to some
bigger box ;). This small iron box have inside RAID controller (Dell uses
in this box LSI Logic SAS MegaRAID based ctrl). Anykind combinations on
controler level RAID was slower than using this as plain JBOD with LVM or
MD+LVM. Diffrence between HW and soft RAID was not so big (1-6% depending
on configuration) but allways HW produces worser results (don't ask me
why). Finaly I decide using this disk as four RAID1 luns only because
under Linux I can't read each phisical disk SMART data and protecting this
by RAID on controller level and collecting SNMP traps from DRAC card was
kind of worakaround for this (in my case it will be better constanlty
monitor disk healt and collesting some SMART data for observe trends on
for example zabbix graphs for try predict some faults using triggers). On
top of this was configured diffrent types of volumes on LVM level (some
with stripping some without, some with bigger some with smaller chunk
size).

But .. in case ZFS diffrences can be better visable.
Q: why ?
A: because most of HW RAID controlers (nevermind is it small/simple
internal HW controler for DAS sotorage or advances in storage processor in
dedicated FC array) are _optimized_ for classic FS workloads but .. ZFS
uses bunch of devices in completly diffrent way/characteristics. If you
will see flashing LEDs on box with disk first time configurad for classic
RAID<any_level> (nevermind soft or hw) and on second time configured for
ZFS you will see kind of organoleptic diffrence.
And yes .. ZFS may be kind of problem for some HW vendors ;)

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*