Understanding Storage Types, Content, and Drive Size

SnAkEhIpS

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Aug 20, 2018
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Backgroud:

I've installed PVE on a standalone node, not a cluster. The physical ssd is 232.89 GiB as viewed from "Disks" under my node (named PVE). During the installation process I/it created:

1. local (pve): Content = VZDump backup file, ISO image, Container tempate > Type = Directory > Size = 56.84GiB
2. local-lvm(pve): Content = Disk image, Container > Type = LVM-Thin > Size = 150.64 GiB
3. local-lvm2(pve): Content = Disk Image, Container > Type = LVM > Size = 232.63 GiB

Nothing above is a typo. I'm new to Linux and Proxmox. I've successfully installed Cisco VIRL, Kubuntu, and Windows with paraviritualized drivers, so I'm not completely daft. I just need some help wrapping my head around storage.

I recently added a 500GiB as follows:
pve02(pve): Content = Disk Image, Container > Type = LVM > Size = 465.76

I need some advice. I'd like to maximize my storage utilization. I will be running linked clones and containers, so if I understand what I've read correctly, I need more LVM-Thin storage than LVM as the former supports snapshots and clones. The advantage of LVM however is that it can be shared. I do need some shared storage.

Question:

When I activated the 500GiB drive, I didn't put it in the same Volume Group as the others. In retrospect, I think I should have done so. I also think that I should have made it LVM-Thin. Is there any advantage or disadvantage to leaving the larger drive in a separate Volume Group? If I want to "do it over", what is the easiest way? Is it possible to take the existing LVM-Thin volume (#2) and combine it with my pve02 volume? Why does #3 show nothing under Contents yet 93.19% usage under Summary?
 
The advantage of LVM however is that it can be shared. I do need some shared storage.
unrelated to the question but note: this is local storage and not shared, so this does not play a role here (a shared lvm would be on an iscsi lun for example)

When I activated the 500GiB drive, I didn't put it in the same Volume Group as the others. In retrospect, I think I should have done so. I also think that I should have made it LVM-Thin. Is there any advantage or disadvantage to leaving the larger drive in a separate Volume Group?
you probably don't want 2 disks in the same volume group/thin pool since this is like putting them into raid0; if one of them goes, the group/thin pool is broken (not really with lvm since it does not stripe by default afaik, but with lvm thin the blocks are only allocated when they are needed so it can happen that you have a vmdisk stretch over both disks)

I also think that I should have made it LVM-Thin.
this is still possible and easy, since a thinpool is simply a special logical volume inside a volume group (see 'man lvmthin')

Why does #3 show nothing under Contents yet 93.19% usage under Summary?
because the whole disk is used as a lvm volume group where:

~57GiB is taken up by root (/)
~151GiB is taken up by the thinpool (the local-lvm storage)
(~57+~151)/(~233) = ~89% so that adds up (swap is probably there too for the missing few percent)

with lvm an allocated logical volume already takes up the space, regardless how much of it is already used

i hope this answers your questions
 
Thank you very much for the clarification. I think I did break something, but it's not something I changed with the disks. I was waiting to hear back. Sorry for my own late response. Work has been relentless. Today I've tried to login via my web browser and I get "Firefox can’t establish a connection to the server at 192.168.0.2:8006." I can ping the server and I can logon to it from the console as well as SSH. Nothing has changed on my network either, but I must have done something. Not sure where to start, but I'll look in the forum and Google.
 
Update. I restarted my server. I can now only login at the console. It is connecting via SSH, but it keeps telling me that my password is incorrect. I tried the CAPS LOCK a few times and no change. I'm not using the keypad, rather the number keys. I've cleared my browser cache and I even tried a private browsing window. Odd. Still digging...
 
I resolved the connectivity issue. I installed an update to CentOs and both my Ethernet and WiFi adapter were rendered enabled. Simply disabling my Ethernet adapter (as my only connection to Proxmox is via WiFi) resolved the issue.
 
you probably don't want 2 disks in the same volume group/thin pool since this is like putting them into raid0; if one of them goes, the group/thin pool is broken (not really with lvm since it does not stripe by default afaik, but with lvm thin the blocks are only allocated when they are needed so it can happen that you have a vmdisk stretch over both disks)
So if I understand you correctly, this would potentially break anything that extends across 2 or more disks in a volume group/thin. In practice, VM's and file storage alike could be lost? If that be the case, then only on physical disk per LVM is recommended?
 
Seems contrary to the whole design of LVM, but then again we are only speaking of blocks crossing physical disks, correct?
 
So if I understand you correctly, this would potentially break anything that extends across 2 or more disks in a volume group/thin. In practice, VM's and file storage alike could be lost? If that be the case, then only on physical disk per LVM is recommended?
Seems contrary to the whole design of LVM, but then again we are only speaking of blocks crossing physical disks, correct?

again, spanning a vg over multiple disks is like using RAID0 (aka "suicide raid")
so if a lv is spanning multiple disks and you lose one of them, the lv is most likely gone
 
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