Extreme Raid Growth

linear · Apprentice Joined: 12 Aug 2004 Posts: 222

OK, so heres the trick:

The challenge: A growable partition and filesystem setup for ultra large arrays.

The hiccup: Pretend we do not have LVM2... because I do not know it well enough to make it happen "RIGHT NOW"

I have 2 devices:

/dev/sda 7.5TB hw RAID5 on AMCC 9550-12
/dev/sdb 7.5TB hw RAID5 on AMCC 9550-12

I raid them together with:

HeissFuss · Guru Joined: 11 Jan 2005 Posts: 414

LVM2 does online resizing, so if your FS also supports it you don't even need to unmount to extend or shrink your partitions.

linear · Apprentice Joined: 12 Aug 2004 Posts: 222

Good point and online growth is a nice feature that is worth having.

When I went strafing for quick and dirty answers, LVM2 was my first choice. I have not used it before but as I went through docs I found myself a little overwhelmed with information that was not relevant to me and provided what looked like overly complex answers to a simple problem. Granted it may have been my choice of docs, but I read what I could find.

If anyone has some quick and dirty howtos on seting up LVM in the fashion I need I would be most appreciative. My needs are to be able to continually grow a volume over time. I do not need to segment it. I just need to concat a bunch of iSCSI targets and be able to add on more later.

HeissFuss · Guru Joined: 11 Jan 2005 Posts: 414

This guide has a section on setting up LVM2. http://gentoo-wiki.com/Installing_on_LVM2_And_Raid5#Creating_LVM2
You can skip the section on software raid.

In a nutshell:

add all physical devices with pvcreate
add all pvcreated devices with vgcreate to a new volume group
create a logical volume with lvcreate which will contain your entire volume group.
format the LV with your FS of choice.

To add a device, pvcreate /dev/device
use vgextend to add the device to your volume group
use lvextend to expand the logical partition by the additional size
grow your FS

linear · Apprentice Joined: 12 Aug 2004 Posts: 222

Your nutshell was exactly what I needed to jump into LVM. Thank you kindly.

I will be consuming LVM resources on the internet and hoped I might put forwad a few questions for varied points of view or pointers to more focused information.*

What is recovery of LVM like if the managing OS goes belly up?

Where is it's config stored, etc?

Are there known recovery issues?

What can happen if the underlying discs unexpectly drop such as when an iSCSI device is interrupted by a network cable being unplugged?

If I have ONLY a single box mount a logical volume, can I safely share out that mount with samba or NFS to multiple users?

###

* I know I can get the best answers from an LVM and/or iSCSI mailing list, and I will seek them there too. I figure, though, that if I had this question, other gentoo users may also, and the richer the questions and answers on our forums, the richer the community is as a whole.

HeissFuss · Guru Joined: 11 Jan 2005 Posts: 414

The config is stored on the disks. There's also a tool you can use to make backups of that data in case you lose the device it's stored on.

I'm not sure how it would react if a linear device went missing. I think you'd just get read/write timeouts until you could get it back up, though you'd hope that it'd crash. Since it's linear it'd also depend on which section of the device you were trying to access.

As for sharing the volume I don't see any problems that would be different from any other shared volume.

If you find any answers please post them here. I'd like to know also.