Question on RAID 10 setup

Question on RAID 10 setup

[Dylan Distasio]

Hi all-

I would like to put together a RAID10 array utilizing 2x1TB drives and
2x500 gig drives I have in my home Linux server.  Is the best way to do
this to create 2 separate RAID1 arrays, one for each set of drives, and
then a RAID0 array made up of the RAID1 ones?   I just wanted to verify
that I am going about this correctly, and also get input on whether
there are any disadvantages to this setup.  I would prefer not to split
these up into two separate RAID10 arrays because I want the combined
space available under one.   Thanks for any comments.

-Dylan
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Re: Question on RAID 10 setup

[John Robinson]

On 24/03/2009 22:15, Dylan Distasio wrote:
> Hi all-
> 
> I would like to put together a RAID10 array utilizing 2x1TB drives and
> 2x500 gig drives I have in my home Linux server.  Is the best way to do
> this to create 2 separate RAID1 arrays, one for each set of drives, and
> then a RAID0 array made up of the RAID1 ones?   I just wanted to verify
> that I am going about this correctly, and also get input on whether
> there are any disadvantages to this setup.  I would prefer not to split
> these up into two separate RAID10 arrays because I want the combined
> space available under one.   Thanks for any comments.

I think you can mix drive sizes under md RAID-10 - much as you're 
proposing to above with your RAID-0 of different-sized RAID-1s - and md 
will just do the Right Thing. I'd go for testing that and play with 
layouts (near, far, offset) to suit your requirements before worrying 
about setting up RAID 1+0.

Actually with your hardware I'd probably set up a 1TB RAID-0 with the 
500G drives then make a RAID-5 from the 3 1TB devices (2 raw drives plus 
one md RAID-0). If you can be bothered try benchmarking that too; as 
well as giving you more storage I think it'll probably match the RAID-10 
or RAID 1+0 for performance.

Cheers,

John.

Re: Question on RAID 10 setup

[Keld Jørn Simonsen]

On Tue, Mar 24, 2009 at 11:48:49PM +0000, John Robinson wrote:
> On 24/03/2009 22:15, Dylan Distasio wrote:
> >Hi all-
> >
> >I would like to put together a RAID10 array utilizing 2x1TB drives and
> >2x500 gig drives I have in my home Linux server.  Is the best way to do
> >this to create 2 separate RAID1 arrays, one for each set of drives, and
> >then a RAID0 array made up of the RAID1 ones?   I just wanted to verify
> >that I am going about this correctly, and also get input on whether
> >there are any disadvantages to this setup.  I would prefer not to split
> >these up into two separate RAID10 arrays because I want the combined
> >space available under one.   Thanks for any comments.
> 
> I think you can mix drive sizes under md RAID-10 - much as you're 
> proposing to above with your RAID-0 of different-sized RAID-1s - and md 
> will just do the Right Thing. I'd go for testing that and play with 
> layouts (near, far, offset) to suit your requirements before worrying 
> about setting up RAID 1+0.

Hmm, the raid 0 will only use the space of all partitions that is equal
to the smallest partition, that is the 500 gig drives. I think you better
then only ude 500 gig partitions on the 1 TB disks for anything that
is combined with the 500 gig disks.


> Actually with your hardware I'd probably set up a 1TB RAID-0 with the 
> 500G drives then make a RAID-5 from the 3 1TB devices (2 raw drives plus 
> one md RAID-0). If you can be bothered try benchmarking that too; as 
> well as giving you more storage I think it'll probably match the RAID-10 
> or RAID 1+0 for performance.

In my book I would consider 2 setups:

1.  a raid5 of 4 500 gig partitions, total 1,5 GB plus a raid10,f2 of
two 500 gig partitions, total  2.0 GB

2. a raid10,f2 of 4 500 gig partitions, total 1.0 GB plus a raid10,f2 of
two 500 gig partitions, total  1.5 GB.

A small comparison table with my 2 scenarios, your own suggestion
and john robisons:

                                size     perf-rd    perf-wr
4x500 raid5     + 0.5 f2        1.5+0,5    3         3
4x500 raid10,f2 + 0.5 f2        1.0+0.5    4         2
4x500 raid1+0   + 0,5 f2        1.0+0.5    2         2
2x1tb+(500+500) raid5           2.0        2         2

So based on what your prefer, like most space vs most read or write
performance, each of these configurations have something to offer.

Best regards
keld

Re: Question on RAID 10 setup

[Neil Brown]

On Tuesday March 24, john.robinson@anonymous.org.uk wrote:
> On 24/03/2009 22:15, Dylan Distasio wrote:
> > Hi all-
> > 
> > I would like to put together a RAID10 array utilizing 2x1TB drives and
> > 2x500 gig drives I have in my home Linux server.  Is the best way to do
> > this to create 2 separate RAID1 arrays, one for each set of drives, and
> > then a RAID0 array made up of the RAID1 ones?   I just wanted to verify
> > that I am going about this correctly, and also get input on whether
> > there are any disadvantages to this setup.  I would prefer not to split
> > these up into two separate RAID10 arrays because I want the combined
> > space available under one.   Thanks for any comments.
> 
> I think you can mix drive sizes under md RAID-10 - much as you're 
> proposing to above with your RAID-0 of different-sized RAID-1s - and md 
> will just do the Right Thing.

Incorrect.  RAID-10, as with all levels that provide redundancy and
hot-spares etc, used the same amount of space on all devices.
Only RAID0 and Linear make use of all available space.

>                               I'd go for testing that and play with 
> layouts (near, far, offset) to suit your requirements before worrying 
> about setting up RAID 1+0.
> 
> Actually with your hardware I'd probably set up a 1TB RAID-0 with the 
> 500G drives then make a RAID-5 from the 3 1TB devices (2 raw drives plus 
> one md RAID-0). If you can be bothered try benchmarking that too; as 
> well as giving you more storage I think it'll probably match the RAID-10 
> or RAID 1+0 for performance.

I think that is a very reasonable option, as is the original
suggestion.

NeilBrown

Re: Question on RAID 10 setup

[Bill Davidsen]

Dylan Distasio wrote:
> Hi all-
>
> I would like to put together a RAID10 array utilizing 2x1TB drives and
> 2x500 gig drives I have in my home Linux server.  Is the best way to do
> this to create 2 separate RAID1 arrays, one for each set of drives, and
> then a RAID0 array made up of the RAID1 ones?   I just wanted to verify
> that I am going about this correctly, and also get input on whether
> there are any disadvantages to this setup.  I would prefer not to split
> these up into two separate RAID10 arrays because I want the combined
> space available under one.   Thanks for any comments.
>   

Possibly you are confusing raid10 with raid1+0, and the documentation 
seems to encourage that. You can just use all your drives with raid10 
and mdadm will do the right thing as far as putting mirrors on other drives.

That said, I like the suggestion John made of raid0 to make a third 1TB 
device, then raid5. But be aware that "raid10 -f2" will be as fast or a 
little faster for write, and quite a bit faster for read, at the expense 
of some size. Using raid10 will give you 1.5TB and fast, raid0+5 will 
give you 2TB storage, but somewhat slower. And raid10 will be far faster 
if you should lose a drive and be running in a degraded mode.

Or you could buy a 1TB drive from Newegg for $89 and have even more 
choices. ;-)

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc

"You are disgraced professional losers. And by the way, give us our money back."
    - Representative Earl Pomeroy,  Democrat of North Dakota
on the A.I.G. executives who were paid bonuses  after a federal bailout.