[ale] KVM Storage - Seeking advice

[Lightner, Jeffrey]

RAID is NOT a substitute for backup.   When you mirror in LVM you’re just doing a RAID1 copy.   Anything that happens to the first disk (e.g. accidental deletion of files) will happen to the mirror copy as well.   If the enclosure that contains both drives (e.g. the server itself) gets damaged (e.g. catches on fire) you’re apt to lose both drives at the same time.

You’re to be commended for using LVM and LVM mirroring but that doesn’t mean you shouldn’t also have a way to back up the data to something external to your system.


From: Ale <ale-bounces at ale.org> On Behalf Of Bryan L. Gay via Ale
Sent: Tuesday, April 23, 2019 11:28 PM
To: Atlanta Linux Enthusiasts <ale at ale.org>
Subject: Re: [ale] KVM Storage - Seeking advice

I've used LVM method of backing store for VMs for many years, but using multiple drives, NOT the old-school mirroring of drives. I configure important LVs to be replicated onto separate PVs:

lvconvert --type=raid1 -m1 volgroupname/lvname /dev/additionalpvname
(careful not to do this to your boot LV unless you know what you're doing - especially if you're an Arch user)

...haven't needed to use thin provisioning, as there's never been a disk space concern.

This allows me to get through drive failures. I've had all of my drives in my server die one at a time. I replace the dead drive with another (bigger) drive, make it a PV, add it to the VG, and off to the races. I'm still running the same VMs, on the same server, on the same LVs, but none of the drives in the server are the original drives. I've had very minimal downtime. It just depends on HOW the bad drive fails. I've replaced the motherboard/CPU/RAM, etc., on this server a couple of times, but all I have to do is power it on and everything boots right back to where it was with no fuss other than the onboard NIC device name needing to be updated for the network to come up. The OS has been upgraded from Debian version to version over the years just to keep it current, which is why I abandoned CentOS years ago.

On Sun, Apr 14, 2019 at 12:43 PM DJ-Pfulio via Ale <ale at ale.org<mailto:ale at ale.org>> wrote:
Thanks for the notes.

Decided to try out both methods. LVM does provide some great flexibility.

Moving the img/qcow2 files over would have been a tiny bit easier, plus
I know exactly how to do that.

On 4/14/19 10:02 AM, Phil Turmel via Ale wrote:
> On 4/12/19 11:04 AM, DJ-Pfulio via Ale wrote:
>> Background
>> ----------
>> I'm setting up a new KVM VM system. It will run 10-30 VMs, but only 15
>> will be core.
>
> Sounds a lot like my office kit.
>
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