[SATLUG] fileserver SATA + RAID question

[Tom Weeks]

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, 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