[SATLUG] filesystems ( was fileserver SATA + RAID question)

[Clif Smith]

Speaking of growing the partitions without downtime, which filesystem are 
you using?

---------- Forwarded message ----------
From: Tom Weeks <tweeksjunk2 at theweeks.org>
Date: Jul 17, 2005 8:21 PM
Subject: Re: [SATLUG] fileserver SATA + RAID question
To: The San Antonio Linux User's Group Mailing List <satlug at satlug.org>

On Sunday 17 July 2005 15:54, Eli wrote:
> lvm is pretty cool, but not something i need.
>
> when using expensive scsi 15,000RPM drives and expensive redundant scsi
> raid controllers, upgrading the array quickly and cheaply is a problem. I
> could see how LVM allows one to simply build a second array on the system
> and add the space to the existing lvm volume.
>
> with commodity hardware, i wouldn't bother with lvm. i just get on
> newegg.com <http://newegg.com>, order a few 400gb pata drives for $258 ea. 
shipped, build a
> new replacement array, move the data over, and be done with it. rsync will
> move the bulk of the data over while the primary system is still
> running(at non peak hours). then pick a time to pull the system offline,
> and rsync the last bit of data that has changed, swap the drives and your
> done.

Ever move 400GB of data on a live filesystems? :)
I would rather not if I didn't have to.

If I decide to grow my /video LVM2 filesystem... I simply get a couple new
external firewire or USB2 drives that I want to merge into my system as a
RAID partition. Go ahead and create the software RAID-1 mirror... then I
just run the following LVM commands to "grow" my 400GB filesystem to use the
new RAID array:
# pvcreate /dev/md4
# vgextend /dev/vg0 /dev/md4
# lvextend -L +400GB /dev/vg0/videoLV
# umount /video && resize_reiserfs /dev/vg0/videoLV && mount /video

Done.. I just grew an existing 400GB filesystem to 800GB, no downtime, no
rsync, and no reboots. Plus I can continue to use my older drives WITH my
newer drives. :)

Doing it your way, what if you want MORE than 800GB? I have a friend at work
who is going to a 1.5TB NFS array. You going to keep your old 800GB array on
line, then build a second 1.5TB RAID array and move you data over? You'll
have to sell all your old drives when you're done. With LVM I can use
whatever I want.. mixing and matching old & new as I go. Drive sizes, RAID
levels, I'm abstracted from all of that. That's what LVM is for..
Abstracting you from the hardware restrictions.

Not trying to be argumentative here.. Just making a case for why to use it 
in
this instance.


> so lvm isn't particularly interesting to me currently, but i think it's
> neat and useful in other situations. raid5 software raid works great imo,
> and with todays proccessors, cpu usage isn't a concern of mine.

You ever have SW RAID-5 on your OS partition(s), and try to boot the system
while still in degraded mode or even worse.. while rebuilding? I have.. Not
"fun" when it takes 50 minutes just to boot.. once...

Not to mention the lack of hardware caching.. (RAM-> disk during power 
outage)

> Going with hardware raid is always an alternative though, we've got the
> 3ware card running raid 5, and it's been flawless, has nice features, and

Yeah.. 3ware rocks. Especially if you can afford their hotswap hardware!


> one thing i do avoid is cheap psuedo raid chipsets that come on mobos and
> pci cards (the ones that do xor on the host cpu, not on the chipset
> itself).

Agreed... I had it on my MythTV's botherboard (MSI mobo with nForce 
chipset)..
After I realized the lack of control that it imposed.. and that I could do 
it
just as well (if not better) w/SWR-1 on Linux.. I opted for the latter.

Tweeks
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