Re: Grow a RAID-10

["Keld Jørn Simonsen" <keld@dkuug.dk>]

On Wed, Jul 02, 2008 at 06:47:31PM -0700, Daniel L. Miller wrote:
> Keld Jørn Simonsen wrote:
> >On Wed, Jul 02, 2008 at 02:56:04PM -0700, Daniel L. Miller wrote:
> >  
> >>I currently have a RAID10 across (4) SATA drives.  It looks like I'm 
> >>going to need to grow in the near future.  Any tips for a procedure for 
> >>this?  My current plan:
> >>
> >>1.  Add a PCI SATA controller (MB had 4 SATA + 4 RAID SATA, it's a Tyan 
> >>MB with a NFORCE chipset, I'm not sure if I want/can use the RAID SATA 
> >>ports as plain SATA connections).
> >>    
> >
> >Why not use the mobo raid sata ports? They are probably faster than a
> >controller on the pci bus. What kind of pci bus do you have?
> >
> >  
> My mistake.  Confused this one with another system.  Only have 4 ports 
> available.  I did have the option of using the Nvidia RAID - which I did 
> NOT enable.

Yes, it is fine not to use the two on-board raid controllers in raid
mode, but just to use SW raid on them. I have a similar mobo with 2
sata controllers and the ability to attach 8 sata drives, which I have
all been using to run SW raid, and I have not experienced any problems
yet with this setup.

I understand that your mobo has 4 onboard sata connections, and that
these are already in use for the current array.

> What "kind" of pci bus?  Don't understand the question.  If it matters, 
> it's a Tyan S2892, a "Thunder K8SE".  nForce Pro2200 and AMD8131 PCI-X 
> chipsets.

So it has both PCI-X bus and PCI-E bus. You want to attact 2 more drives 
and you need a sata controller. This could probably both be attached via
the PCI-X bus and the PCI-E bus. It seems like the PCI-X bus - with a
133 MHz possibility counld be the faster of the 2, but given you will
only have 2 more drives, both PCI-X and PCI-E are prossibilties.

> >PCI-E 1x is likely to be too slow for a 4-drive raid10,f2 array.
> >My 4-drive raid10,f2 delivers about 320 MB/s and newer disks should be
> >able to deliver 360 MB/s - well above the 250 MB/s that a PCI-E 1x can
> >deliver. 
> >
> >  
> >>2.  Add 2 more drives - not necessarily the same size as the existing 
> >>(they were all 4 the same)
> >>
> >>3.  Execute "mdadm --grow /dev/md0"
> >>    
> >
> >What kind of raid10 do you have?> 
> >  
> I don't understand this question either.
> 
> mdadm --detail /dev/md0
> /dev/md0:
>        Version : 00.90.03
>  Creation Time : Tue Oct  3 19:11:53 2006
>     Raid Level : raid10
>     Array Size : 312581632 (298.10 GiB 320.08 GB)
>  Used Dev Size : 156290816 (149.05 GiB 160.04 GB)
>   Raid Devices : 4
>  Total Devices : 4
> Preferred Minor : 0
>    Persistence : Superblock is persistent
> 
>    Update Time : Wed Jul  2 18:46:15 2008
>          State : clean
> Active Devices : 4
> Working Devices : 4
> Failed Devices : 0
>  Spare Devices : 0
> 
>         Layout : near=2, far=1
>     Chunk Size : 32K
> 
>           UUID : 9d94b17b:f5fac31a:577c252b:0d4c4b2a
>         Events : 0.10941692
> 
>    Number   Major   Minor   RaidDevice State
>       0       8        0        0      active sync   /dev/sda
>       1       8       16        1      active sync   /dev/sdb
>       2       8       32        2      active sync   /dev/sdc
>       3       8       48        3      active sync   /dev/sdd

I was takling about the layout, and you have a n2 layout (standard
raid10 - near=2). You may benefit from a raid10,f2 layout, as this has faster 
read capabilities, but I think it is not possible on the fly to
rearrange a raid10,n2 array to a raid10,f2 array.

Given that you have a raid10,n2 layout, the speeds of the busses are not
so important, as raid10,n2 cannot deliver that high performance. 
I would expect less than 100 MB/s coming out of your 2 extra disks.

What is the use for your raid? is it a database, a file server, a web
server or the like?

Best regards
keld
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