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"Mag Gam" 06-07-2008 12:27 PM

RAID for large disks
 
I have a RAID controller with 256MB of on board cache and its connected to 12 500GB SATA disks. I am planning to create 2 RAID groups (6 disks each), but I don't know what is the optimal stripe size should be.


Also, once I stripe on the RAID controller I am planning to use LVM. Is striping a good idea? What should I consider for the filesystem?


TIA

"Damon L. Chesser" 06-07-2008 01:59 PM

RAID for large disks
 
On Sat, 2008-06-07 at 08:27 -0400, Mag Gam wrote:
>
> I have a RAID controller with 256MB of on board cache and its
> connected to 12 500GB SATA disks. I am planning to create 2 RAID
> groups (6 disks each), but I don't know what is the optimal stripe
> size should be.

Are you going to use the RAID controller to make the raid (ie, they will
be hardware raid and the machine and the OS will not know of it)? If
so, I would go with the controller defaults with out overriding reasons
to change them. One such reason I can think of is an application such
as oracle which has very detailed instructions on what kind of
strip/raid you need for a particular use.
>
> Also, once I stripe on the RAID controller I am planning to use LVM.
> Is striping a good idea?
This, I don't know.
> What should I consider for the filesystem?

Again, it depends on your use. Lots of real big files, you might want
something besides ext3. Lots of little or just "normal" files, ext3
should work just fine for you. There are some file system "experts" on
this list that can fill in the details. As a disclaimer, I have only
used ext3 and have never had to use anything different. But again, your
"Killer app" might have very specific requirements (again, oracle is
very specific in it's recommendations and I assume any good app will
tell you the optimum set up for it's self) however here are some things
to read to fill in the time for you :)
http://fsbench.netnation.com/ <--Performance comparison: Linux
filesystems.

http://en.wikipedia.org/wiki/Comparison_of_file_systems

http://linuxreviews.org/sysadmin/filesystems

http://www.linfo.org/filesystem.html

No matter what FS you choose, I would NOT deviate from having a /boot in
ext3. The filesystem has very good recovery tools and is well
documented. I might also not use anything but ext3 for the / as well
and put /kill_app on the optimal type of fs for it's self. If XFS is
the best for your app, having /boot and / in ext3 will not affect the
app. This might be a prejudice I have since I am very comfortable
working in ext3 and not so in say, Reisers, especially in file recovery
operations or resizing.

HTH
--
Damon L. Chesser
damon@damtek.com
http://www.linkedin.com/in/dchesser

"Mag Gam" 06-07-2008 03:32 PM

RAID for large disks
 
Damon,

I haven't even approached the file system level yet. The application is a basic fileserver which will host our professor's mechanical engineering images. These images can be anywhere from 20MB to 300MB so I would consider them "normal files".


I am hoping some hardware people can chime in about the RAID configuration first. I have plenty of RAM on the server (12GB), and a fast RAID controller so I would like to get this going first then I will worry about the file system. Unless, people feel this is a holistic approach.


Any thoughts?

*

On Sat, Jun 7, 2008 at 9:59 AM, Damon L. Chesser <damon@damtek.com> wrote:

On Sat, 2008-06-07 at 08:27 -0400, Mag Gam wrote:

>

> I have a RAID controller with 256MB of on board cache and its

> connected to 12 500GB SATA disks. I am planning to create 2 RAID

> groups (6 disks each), but I don't know what is the optimal stripe

> size should be.



Are you going to use the RAID controller to make the raid (ie, they will

be hardware raid and the machine and the OS will not know of it)? *If

so, I would go with the controller defaults with out overriding reasons

to change them. *One such reason I can think of is an application such

as oracle which has very detailed instructions on what kind of

strip/raid you need for a particular use.

>

> Also, once I stripe on the RAID controller I am planning to use LVM.

> Is striping a good idea?

This, I don't know.

> *What should I consider for the filesystem?



Again, it depends on your use. *Lots of real big files, you might want

something besides ext3. *Lots of little or just "normal" files, ext3

should work just fine for you. *There are some file system "experts" on

this list that can fill in the details. *As a disclaimer, I have only

used ext3 and have never had to use anything different. *But again, your

"Killer app" might have very specific requirements (again, oracle is

very specific in it's recommendations and I assume any good app will

tell you the optimum set up for it's self) however here are some things

to read to fill in the time for you :)

http://fsbench.netnation.com/ <--Performance comparison: Linux

filesystems.



http://en.wikipedia.org/wiki/Comparison_of_file_systems



http://linuxreviews.org/sysadmin/filesystems



http://www.linfo.org/filesystem.html



No matter what FS you choose, I would NOT deviate from having a /boot in

ext3. *The filesystem has very good recovery tools and is well

documented. *I might also not use anything but ext3 for the / as well

and put /kill_app on the optimal type of fs for it's self. *If XFS is

the best for your app, having /boot and / in ext3 will not affect the

app. *This might be a prejudice I have since I am very comfortable

working in ext3 and not so in say, Reisers, especially in file recovery

operations or resizing.



HTH

--

Damon L. Chesser

damon@damtek.com

http://www.linkedin.com/in/dchesser

"Damon L. Chesser" 06-07-2008 03:49 PM

RAID for large disks
 
On Sat, 2008-06-07 at 11:32 -0400, Mag Gam wrote:
> Damon,
>
> I haven't even approached the file system level yet. The application
> is a basic fileserver which will host our professor's mechanical
> engineering images. These images can be anywhere from 20MB to 300MB so
> I would consider them "normal files".
>
> I am hoping some hardware people can chime in about the RAID
> configuration first. I have plenty of RAM on the server (12GB), and a
> fast RAID controller so I would like to get this going first then I
> will worry about the file system. Unless, people feel this is a
> holistic approach.
>
> Any thoughts?

Yes, two.
1. If this is just a file server, then take the hardware defaults, they
will serve you well (I am a hardware person). All my experience has
been on Dell and that is the "official" Dell line unless your app says
otherwise.

2. If you top post on this list, people will respond (in a frenzy)
about that. On this list, the accepted is to: a. bottom post, or, b.
post in line (as I did to your OP)

I don't care how you reply, however it is easier to read the flow with
bottom posting or in-line posted as I can see what came before and the
response. Other wise I have to read what you posted, then scroll down
to find what you are responding to. Again, I don't care, but some here
do and you will alienate them by top posting.

Concerning the stripe in LVM, I don't know and I am waiting on someone
who does know so that I can learn with you :)

HTH


--
Damon L. Chesser
damon@damtek.com
http://www.linkedin.com/in/dchesser

Mike Bird 06-07-2008 03:55 PM

RAID for large disks
 
On Sat June 7 2008 08:32:27 Mag Gam wrote:
> I haven't even approached the file system level yet. The application is a
> basic fileserver which will host our professor's mechanical engineering
> images. These images can be anywhere from 20MB to 300MB so I would consider
> them "normal files".
>
> I am hoping some hardware people can chime in about the RAID configuration
> first. I have plenty of RAM on the server (12GB), and a fast RAID
> controller so I would like to get this going first then I will worry about
> the file system. Unless, people feel this is a holistic approach.

FWIW, I work in the other direction. Consideration of applications
and data - and of performance, reliability and simplicity - lead to
consideration of possible plans for filesystems, swap, LVM, and RAID.

You might also want to Google or check the list archives for a
discussion of the relative merits of s/w versus h/w RAID.

--Mike Bird


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Ron Johnson 06-07-2008 04:15 PM

RAID for large disks
 
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 06/07/08 07:27, Mag Gam wrote:
>
> I have a RAID controller with 256MB of on board cache and its connected
> to 12 500GB SATA disks. I am planning to create 2 RAID groups (6 disks
> each), but I don't know what is the optimal stripe size should be.

That's very controler-specific. Read the manual.

> Also, once I stripe on the RAID controller I am planning to use LVM. Is
> striping a good idea? What should I consider for the filesystem?

Striping is a GREAT idea IFF you want serious speed, but don't care
about your data. If one of the disks goes flaky, *all* the data on
the stripeset goes poof.

So, *never* use striping on a production server!! Unless you hate
the company, are vindictive, and are about to leave.

Otherwise, use RAID 0, 10, 0+1 or 5.

If you make huge RAID sets, I don't see the purpose of LVM. OTOH,
if you make 6 mirror sets, use LVM to make a 6 "device" unit.

Also, Damon is correct about booting. In fact, I'd have a separate
boot device.

Lastly, to what media are you going to back all this data up? How
frequently?

- --
Ron Johnson, Jr.
Jefferson LA USA

"Kittens give Morbo gas. In lighter news, the city of New New
York is doomed."
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"Damon L. Chesser" 06-07-2008 04:38 PM

RAID for large disks
 
On Sat, 2008-06-07 at 11:15 -0500, Ron Johnson wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 06/07/08 07:27, Mag Gam wrote:
> >
> > I have a RAID controller with 256MB of on board cache and its connected
> > to 12 500GB SATA disks. I am planning to create 2 RAID groups (6 disks
> > each), but I don't know what is the optimal stripe size should be.
>
> That's very controler-specific. Read the manual.
>
> > Also, once I stripe on the RAID controller I am planning to use LVM. Is
> > striping a good idea? What should I consider for the filesystem?
>
> Striping is a GREAT idea IFF you want serious speed, but don't care
> about your data. If one of the disks goes flaky, *all* the data on
> the stripeset goes poof.
>
> So, *never* use striping on a production server!! Unless you hate
> the company, are vindictive, and are about to leave.
>
> Otherwise, use RAID 0, 10, 0+1 or 5.
>
> If you make huge RAID sets, I don't see the purpose of LVM. OTOH,

for one, if you make a bad partition choice. With LVM, you can shrink
one and grow the other as needed.

> if you make 6 mirror sets, use LVM to make a 6 "device" unit.
>
> Also, Damon is correct about booting. In fact, I'd have a separate
> boot device.
>
> Lastly, to what media are you going to back all this data up? How
> frequently?
>
> - --
> Ron Johnson, Jr.
> Jefferson LA USA

To back up Ron's input:

http://www.linuxjunkies.org/html/LVM-HOWTO.html#s8 it is a bit dated,
but the info is good.


--
Damon L. Chesser
damon@damtek.com
http://www.linkedin.com/in/dchesser

"Mag Gam" 06-07-2008 04:52 PM

RAID for large disks
 
With the RAID array I am planning to use RAID 5 so my data is still protected. My confusion is going with RAID striping (picking the right size). Also, Does the filesystem layout need to be specific when I do striping? If I am using 128k stripes, should I start my filesystem on 129k and end with max-(128+1k)?



On Sat, Jun 7, 2008 at 12:38 PM, Damon L. Chesser <damon@damtek.com> wrote:

On Sat, 2008-06-07 at 11:15 -0500, Ron Johnson wrote:

> -----BEGIN PGP SIGNED MESSAGE-----

> Hash: SHA1

>

> On 06/07/08 07:27, Mag Gam wrote:

> >

> > I have a RAID controller with 256MB of on board cache and its connected

> > to 12 500GB SATA disks. I am planning to create 2 RAID groups (6 disks

> > each), but I don't know what is the optimal stripe size should be.

>

> That's very controler-specific. *Read the manual.

>

> > Also, once I stripe on the RAID controller I am planning to use LVM. Is

> > striping a good idea? What should I consider for the filesystem?

>

> Striping is a GREAT idea IFF you want serious speed, but don't care

> about your data. *If one of the disks goes flaky, *all* the data on

> the stripeset goes poof.

>

> So, *never* use striping on a production server!! *Unless you hate

> the company, are vindictive, and are about to leave.

>

> Otherwise, use RAID 0, 10, 0+1 or 5.

>

> If you make huge RAID sets, I don't see the purpose of LVM. *OTOH,



for one, if you make a bad partition choice. *With LVM, you can shrink

one and grow the other as needed.



> if you make 6 mirror sets, use LVM to make a 6 "device" unit.

>

> Also, Damon is correct about booting. *In fact, I'd have a separate

> boot device.

>

> Lastly, to what media are you going to back all this data up? *How

> frequently?

>

> - --

> Ron Johnson, Jr.

> Jefferson LA *USA



To back up Ron's input:



http://www.linuxjunkies.org/html/LVM-HOWTO.html#s8 *it is a bit dated,

but the info is good.





--

Damon L. Chesser

damon@damtek.com

http://www.linkedin.com/in/dchesser

Ron Johnson 06-07-2008 07:40 PM

RAID for large disks
 
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


The other reason why I hate gmail is that it, like Outlook,
naturally top-posts...

On 06/07/08 11:52, Mag Gam wrote:
> With the RAID array I am planning to use RAID 5 so my data is still
> protected. My confusion is going with RAID striping (picking the right
> size).

What does the controller manual say?

> Also, Does the filesystem layout need to be specific when I do
> striping? If I am using 128k stripes, should I start my filesystem on
> 129k and end with max-(128+1k)?

Huh? Do you mean partition layout?

>
> On Sat, Jun 7, 2008 at 12:38 PM, Damon L. Chesser <damon@damtek.com
> <mailto:damon@damtek.com>> wrote:
>
> On Sat, 2008-06-07 at 11:15 -0500, Ron Johnson wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > On 06/07/08 07:27, Mag Gam wrote:
> > >
> > > I have a RAID controller with 256MB of on board cache and its
> connected
> > > to 12 500GB SATA disks. I am planning to create 2 RAID groups (6
> disks
> > > each), but I don't know what is the optimal stripe size should be.
> >
> > That's very controler-specific. Read the manual.
> >
> > > Also, once I stripe on the RAID controller I am planning to use
> LVM. Is
> > > striping a good idea? What should I consider for the filesystem?
> >
> > Striping is a GREAT idea IFF you want serious speed, but don't care
> > about your data. If one of the disks goes flaky, *all* the data on
> > the stripeset goes poof.
> >
> > So, *never* use striping on a production server!! Unless you hate
> > the company, are vindictive, and are about to leave.
> >
> > Otherwise, use RAID 0, 10, 0+1 or 5.
> >
> > If you make huge RAID sets, I don't see the purpose of LVM. OTOH,
>
> for one, if you make a bad partition choice. With LVM, you can shrink
> one and grow the other as needed.
>
> > if you make 6 mirror sets, use LVM to make a 6 "device" unit.
> >
> > Also, Damon is correct about booting. In fact, I'd have a separate
> > boot device.
> >
> > Lastly, to what media are you going to back all this data up? How
> > frequently?
> >
> > - --
> > Ron Johnson, Jr.
> > Jefferson LA USA
>
> To back up Ron's input:
>
> http://www.linuxjunkies.org/html/LVM-HOWTO.html#s8 it is a bit dated,
> but the info is good.

- --
Ron Johnson, Jr.
Jefferson LA USA

"Kittens give Morbo gas. In lighter news, the city of New New
York is doomed."
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"Andrew M.A. Cater" 06-07-2008 08:27 PM

RAID for large disks
 
On Sat, Jun 07, 2008 at 12:52:24PM -0400, Mag Gam wrote:
> With the RAID array I am planning to use RAID 5 so my data is still
> protected. My confusion is going with RAID striping (picking the right
> size). Also, Does the filesystem layout need to be specific when I do
> striping? If I am using 128k stripes, should I start my filesystem on 129k
> and end with max-(128+1k)?
>

You have four or five considerations.

You mentioned you were going to use your 12 disks as two RAID arrays.

If one is going to be for your data and one for a backup of that data -
2 x RAID 5 and then RAID1 [5 x 500 = ~2.5TB mirrored].

If you need maximum data storage - all your disks in one array in RAID
5.

11 x 500, one spare - 5.5TB but you rely on the spare :)

If you need data resilience - all your disks in one array in RAID 6 or
RAID 10

Hardware RAID control is lovely - but you may need battery backup on
some cards to avoid problems on delayed writes. Hardware RAID control
also ties you to one manufacturer's cards and/or recovery utilities if a
RAID fails and you have to recover data.

If you go the hardware route: take the card defaults.

Linux mdadm works well and, under some circumstances, can approach the
performance of a dedicated hardware RAID card - disks can be swapped
into any Linux box to recover the RAID.

You can then add LVM on top.

HTH,

Andy


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