Software/ Hardware RAID info

Software/ Hardware RAID info

[Rick Bragg]

Hi,

I am new to setting up RAID arrays, and I have experimented in the past
with software only RAID, but now I have a new Dell PowerEdge 1900 with a
SAS RAID controller daughter card.  

My question is: What is the difference in tools that I will use to
create and manage this hardware array?  Can I still use all the same
techniques and tools such as mdadm, LVM2, and GParted to manage my
array? or is it all in the bios.

Another question is how should I format these disks?  Typically I would
use a root file system, and a swap file system that is twice the size of
my memory.  Since all four of my disks are used for hardware RAID, can I
partition this into 2 array's? one for my root, and the other for
swap...

Any advice into setting this up is greatly appreciated.

Thanks
Rick

RE: Software/ Hardware RAID info

[David Lethe]

The simple answer is that nobody can give you anything but a generic
answer unless you supply much more data.

Basically, you want to consider the RAID controller, logical disk(s),
HBA, file system, kernel settings, cache settings on O/S, disk drivers,
RAID controller, and queue depths, buffer memory, and such ... to
minimize the number of times it has to go to disk.  Are you cpu bound,
or I/O bound, what controllers do you have, 

Do you have 15K.5 SAS disks or are you using SATA drives?  Are you
interested I IOPS or throughput?  Large or small-block, or mixed? Video
streaming ???  Random or sequential?  Where are the hotspots and how big
are they?  Write intensive or read intensive.  What kernel? Using PCI-e,
PCI slots?  Running a mailserver, database, general accounting, video
streaming?  Ifyou have a primary application the system is running, then
first consult the software vendor. They know how their software
interacts with a file system and can generally make decent suggestions.

Effectively, you said you just bought a transportation device to take
things places.  At least by giving me the Dell model I can at least
recommend a train, hovercraft, car, or F16 .. but you certainly didn't
give me anything about destination, how much cargo you have, how quickly
it needs to get there, frequency of trips, or the insurance deductable
(analogy RAID1, RAID5, or RAID6).

I'm a little sarcastic now, sorry, don't really mean it.  You did the
write thing to ask before you set it up.  For what it is worth, if you
got a contract from Dell, then they will typically spend time on the
phone at least helping you figure out the basics. Drop me a private
message and if you want to call me for a few mins, I'll help you out. 

David @ santools ^com

-----Original Message-----
From: linux-raid-owner@vger.kernel.org
[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Rick Bragg
Sent: Friday, April 18, 2008 6:22 PM
To: linux-raid@vger.kernel.org
Subject: Software/ Hardware RAID info

Hi,

I am new to setting up RAID arrays, and I have experimented in the past
with software only RAID, but now I have a new Dell PowerEdge 1900 with a
SAS RAID controller daughter card.  

My question is: What is the difference in tools that I will use to
create and manage this hardware array?  Can I still use all the same
techniques and tools such as mdadm, LVM2, and GParted to manage my
array? or is it all in the bios.

Another question is how should I format these disks?  Typically I would
use a root file system, and a swap file system that is twice the size of
my memory.  Since all four of my disks are used for hardware RAID, can I
partition this into 2 array's? one for my root, and the other for
swap...

Any advice into setting this up is greatly appreciated.

Thanks
Rick

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

RE: Software/ Hardware RAID info

[Peter Grandi]

[ ... ]

>> I am new to setting up RAID arrays, and I have experimented
>> in the past with software only RAID, but now I have a new
>> Dell PowerEdge 1900 with a SAS RAID controller daughter card.

>> My question is: What is the difference in tools that I will
>> use to create and manage this hardware array?  Can I still
>> use all the same techniques and tools such as mdadm, LVM2,
>> and GParted to manage my array? or is it all in the bios.

Either way. Some people prefer hw/BIOS RAID, some people prefer
sw/Linux RAID. I prefer the latter in most cases because of its
flexibility, but the former is simpler to deal with.

>> Another question is how should I format these disks?

My usual generic advice is to use RAID10, unless you really know
what you are doing, and JFS as filesystem on top. You can't go
much wrong with these choices.

I guess that in your case convenience is more important than
flexibility and hw/BIOS RAID10 may be simpler to setup than
sw/Linux RAID10, even if the latter is particularly flexible.

Also I dread to think of people who use LVM2 at all, and in
particular with RAID, as there are many pitfalls, and LVM is
almost always unncessary (except in two cases perhaps, and I
don't think even in those case it makes much sense anymore).

>> Typically I would use a root file system, and a swap file
>> system that is twice the size of my memory.

Simple and flexible.

>> Since all four of my disks are used for hardware RAID, can I
>> partition this into 2 array's? one for my root, and the other
>> for swap...

That sounds very peculiar. Linux swap does not really need RAID,
except perhaps RAID1 for extreme cases.

>> Any advice into setting this up is greatly appreciated.

> The simple answer is that nobody can give you anything but a
> generic answer unless you supply much more data.

So I tried :-).

> [ ... ] You did the write thing to ask before you set it up.
> For what it is worth, if you got a contract from Dell, then
> they will typically spend time on the phone at least helping
> you figure out the basics. [ ... ]

Uhm, I would not suggest asking Dell support for this. More like
suggest finding some good papers on RAID, and some HOWTOs, and
studying them carefully. Storage design is a complex and
difficult subject that might take years of study, not call
centre advice over the phone.

Or just my pithy "can't go much wrong" extremely generic advice
above for those without the time.

Re: Software/ Hardware RAID info

[Keld Jørn Simonsen]

> [ ... ]
> 
> >> Any advice into setting this up is greatly appreciated.

there is a howto for Linux RAID at http://linux-raid.osdl.org/

I wrote a howto at
http://linux-raid.osdl.org/index.php/Preventing_against_a_failing_disk
which looks like it addresses an number of your questions.

Best regards
keld