[olug] The "other" raid utility usage

[Matthew G. Marsh]

On Wed, 23 Apr 2003, Daniel G. Linder wrote:

> Matthew, or anyone else for that matter,
>
>   Has anyone ever tried the filesystem resize "stuff"?  I know that EXT2
>   has some hooks to allow for a filesystem to be resized, but do I have
>   to un-mount that filesystem to do this, or can I do it on the fly (if
>   I have space on the HDD)?  Here is what lead to this question:

Supposedly you can add space on the fly. I have not tried it meself. At
LinuxWorld in 2001 I heard Ted T'so talk about using a patch to mke2fs for
this but I never really followed up.

Your best bet it to use LVM (pick one they are all pretty much the same
although I am partial to IBM's) to create the filesystem. Note that LVM
can create and manipulate filesystem partitions on raid (MD)  devices. LVM
will allow you to merge, split, and do loads of wierd things to the
filesystems. You can even mirror two logical partitions (filesystems)
themselves...

>   Say I am fortunate enough to have a hot-swappable RAID array with five
>   18GB HDDs setup in RAID-5 using 100% of the HDD space.  Years go by,
>   and as drives fail, I replace them but since prices have come down I
>   purchase 36GB HDDs and just leave the remainder un-formatted.  Once
>   all five HDD's have been replaced, I *could* then expand the
>   filesystem and get double the space without rebuilding the
>   partition...  If this were an extremely critical system -- i.e.
>   99.999% uptime is not good enough :) -- then doing the expansion on
>   the fly would be really cool and a big shot in the arm for Linux. :D

Ooog - I would definately only want to try this with LVM - especially on
"critical" filesystems.

> Dan
> (Just trying to scrape together enough $$$ for a *single* larger HDD... :( )

Yeah - funny thing is I could have bought three 200M IDE drives for the
price of the SCSI rack unit but I trust the SCSI rack to be running long
after the IDE's have been in the landfill... O'course that is probably
just my ancient wheezing take on this newfangled stuff... ;-}

Hmmm - if lug ever holds a meeting I can make maybe we can try to put
together a demo of mdadm and LVM in action. Could be fun...

--------------------------------------------------
Matthew G. Marsh,  President
Paktronix Systems LLC
1506 North 59th Street
Omaha  NE  68104
Phone: (402) 553-2288
Email: mgm at midwestlinux.com
WWW:  http://www.midwestlinux.com
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