DS2300 configuration: Striping + mirroring + alternate paths

[Roman Dijanosic]

Greetings all,

I am in a little doubts. Our company bought
array DS2300 (former SC10 if I understand correctly) and new server rp5470. DS2300
will be attached to 5470 server. The intention
in DS2300 is to build striping + mirror + use
alternate paths with LVM. There will be 10 disks in DS2300, so effectively only 5 will
be use in striping.

How to do it (please use
attachments not links to additional docs - any docs on striping + mirroring + alternate paths TOGETHER -not separate with these I am familiar - are welcome)?
What is the suggested sequence of LVM commands
(examples will be the best).

I have read something about bus split mode
and now I am not sure is better to use full
bus mode or split bus mode? Can mirroring
and alternate paths even co-exists (if assumption is that mirroring is best across
SCSI controllers, but also this is "defintion" of alternate paths)? This information is
crucial to me because if I undersood correctly
it involves "hardware intervetion" (O.K. dip switch handling...) which must be done as
first thing (later can not be done as
it "scrambles" device paths).

Thanks for any help in advance.

Roman D.

[Vincent Farrugia]

Hello,

Full bus mode is when you have the controller A accessing ALL harddisks in the ds2300. Controller B also accesses all harddisks, making it good for alternate path.

Split bus mode is when Controller A controls 7 of the harddisks (in your case 5), and controller B controls the other 7 (or 5 in your case). This, though, extinguishes the alternate path.

When you mirror, preferably you mirror across controllers, so as not have IO bottlenecks. So split-bus mode is awesome for this. BUT, you lose the alternate path in this case, so no good.

Else, mirror on the same controller A using full bus mode, having the alternate path, but you'll have performance penalties.

The best way to do it is to buy an additional ds2300. You can mirror across disk arrays in this manner in full-bus mode (2 separate controllers so performance is awesome) allowing alternate paths as well. (The way you want it).

HTH,
Vince

[Roman Dijanosic]

>Full bus mode is when you have the controller >A accessing ALL harddisks in the ds2300. >Controller B also accesses all harddisks, >making it good for alternate path.
>Split bus mode is when Controller A controls >7 of the harddisks (in your case 5), and >controller B controls the other 7 (or 5 in >your case). This, though, extinguishes the >alternate path.
>When you mirror, preferably you mirror across >controllers, so as not have IO bottlenecks. >So split-bus mode is awesome for this. BUT, >you lose the alternate path in this case, so >no good.

Vince,

Thanks for confirming what I thought but I was
definitely not certain and confused.

>Else, mirror on the same controller A using >full bus mode, having the alternate path, but >you'll have performance penalties.

Now my real worry comes. The only way with one DS2300 and to have striping + mirror +
alternate path is to have a mirror across
1 controller... I have to think again about
this. I have to quantify now what is important
to me: mirror or alternate path. If it is
alternate path then this means that only 1
controller will work and what is worse it will have 100% more load. Hmmm... But then again
Ultra160 and OLTP database, should be feasible.

What about LVM commands? If I still make
such configuration is it best to first take
care of alternate links and then for mirror
or vice versa. Striping flags can be I think specified at the same time as mirror flag...
Any suggestion (examples)?

Roman D.

[Vincent Farrugia · Accepted solution]

Hello,

Follow these links:

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x27ebed6464a6d611abdb0090277a778c,00.html

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x768fe7613948d5118fef0090279cd0f9,00.html

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x0d5fc5ea0230d411ade80090279cd0f9,00.html

Seems like you have to use lvcreate -D

HTH,
Vince

[Roman Dijanosic]

Vince,

Thank you for helping me. After re-thinking
I will use bus split mode (so no alternate
paths - they are anyway somehow strange if
you have only 1 array and you want to use
mirrors). After that decision everything
becomes much simpler and clear.

Thread closed.

Roman D.