[ILUG] Highpoint Sata RAID

[John Coleman]

On Fri, 25 Mar 2005 13:58:20 +0000, Niall O Broin <niall at linux.ie> wrote:
> On 25 Mar 2005, at 13:00, John Coleman wrote:
> 
> > With whichever card I buy, I'm going to be putting 3x 400Gig drives in
> > them as one raid5 array, single logical drive, formatted with XFS. I
> > intend to expand this array with more drives down the road but I have
> > a query regarding the array expansion; after plugging in the new
> > drive, I expect the controller to intergrate the drive into the
> > current array, and that the existing logical drive will need to be
> > increased to take advantage of the new space offered.
> > I have 2 concerns regarding this:
> > Firstly, ignoring downtime, will the existing partition on the logical
> > drive remain untouched, with the additional space showing up as
> > unpartitioned dirive space?
> > Secondly, I have never had to change the size of a partition where the
> > data was critical, I assume there are methods in place to expand the
> > existing partition to use the whole logical drive, and that XFS
> > supports expansion in such a way?
> 
> XFS does indeed support expanding a filesystem, with the xfs_growfs
> command. The xfs expansion will be the least of your problems. You need
> to do the following:
> 
> 1) Add the extra disk into the RAID-5 array.
> 2) Increase the size of the partition on which the filesystem lives.
> 3) Extend the filesystem.
> 
> Getting the easy stuff out of the way first, 3) is supported by
> xfs_growfs.
> 
> 2) is a bit of a mess, because you have a disk which has a partition
> table, and suddenly that partition table is wrong and needs changing.
> I've done this on raw disks, and it has worked, and it has failed. LVM
> may be of some help here - a little light reading might be in order :-)
> 
I'd an idea LVM might have to be involved.
> 1) is where Aughrim may be lost. IIRC we had this discussion here a
> while ago. With any RAID cards I have used, adding an extra drive into
> the array means rebuilding the array (because data is striped across
> all disks).

> However, I'm pretty sure that somebody on the list
> mentioned some cards which have some magic means of doing just this. A
> search of the archives might help (I tried, but my google foo is weak).
I'm fairly sure that the LSI card can do it without losing data.
>From my (albeit totally theoretical) understanding, the 3ware and LSI
cards array model looks something like this:
drives on card -> card configures drives into array(s) -> card creates
logical disks on each array -> partition is created on the logical
disk by OS -> partition is formatted by OS

Now, where I can see a problem is in the logical disk on which the
partition-table resides suddenly becoming bigger after the card has
incorporated the new disk into the given array.
Surely this is similar to putting a ghost image on a drive which is
larger than the image? The partition table should update (possibly
through some utility? cfdisk?), then use another utility (xfs_growfs?)
to expand the partition/format the free space?

This part is crucial, otherwise it'll be another while before I get
this array built as I can only afford 3 drives at the moment, but I
plan on having 6-8 (maybe with one as a hot-spare) in the end.
> 
> Last but not least - you mentioned critical data. It'd take a much
> braver man than me to try to do this with valuable data which is not
> safely backed up.
> 
> Niall
> 
> --
> Irish Linux Users' Group
> http://www.linux.ie/mailman/listinfo/ilug/
> 
> 
OT: fakeraid cards are dirty hacks, utterly deplorable. They are only
helping to breed confusion and disinformation amongst consumers who
believe they have a fast/secure raid setup.
An IDE controller lashing together two drives in a container does not
a RAID controller make.

-- 
John Coleman
NUIG, Computer Society