qcow2 vs vmdk

[informant]

Hi,

i have a question.
What do you need fot vm´s: qcow2 or vmdk. What is the difference and what is the size limit?

regards

 

[Patschi]

qcow2 is the file system from KVM itself and vmdk from VMware. I found a nice site, describing qcow2:
http://fedoraproject.org/wiki/Features/KVM_qcow2_Performance

It's up to you, which one you want to use. I don't think, that there is a big performance difference. For example if you have VMware Player/Workstation you can easily integrate the vmdk disk in your VMware VM and start it. I would suggest you to use qcow2 - It's easy to mount qcow2 images in a linux directory with qemu-nbd.

By the way: You also can use raw - this is the fastest of all three formats. But: If you create a 100 GB disk for your VM, the raw-file does use 100 GB on your hostsystem. qcow2 instead is just growing, if you put more data in it.

 

[informant]

Hello Patschi,

thanks for this nice informations. Do you have a information about max filesize of a qcow2 file?

best regards

 

[Patschi]

Found something interested about the qcow2 size limit on Google (in the first three results!):
http://rwmj.wordpress.com/2011/10/03/maximum-qcow2-disk-size/


I guess you never would use the total possible size of 9.223.372 TB on one harddisk-file

 

[informant]

Ok, thanks. I have found same information, but i was not shure, if it was correctly before.

Very thanks and have a nice day.

regards

 

[screenie]

By the way: You also can use raw - this is the fastest of all three formats. But: If you create a 100 GB disk for your VM, the raw-file does use 100 GB on your hostsystem. qcow2 instead is just growing, if you put more data in it.

Proxmox use pre-allocation when creating qcow2 images, so it's also using the the full size on the host system;
This prevents over provisioning of your storages;

 

[Patschi]

I also thought so, but my images with qcow2 just have a size about ~15 GB, but the total harddisk size of the VM is 50 GB.

 

[mir]

If I remember correct qcow2 operates with two kinds of size: Reserved and allocated.
In your case the image has reserved 50GB in the file system but the allocated size amounts to the actual used space at any given point in time.
You should see the difference using df and ls.

 

[screenie]

uh, you are right - never checked with df....
is there a way to check the pre-allocated space of a file-system?

 

[AndrzejL]

Hi, I know its a dead topic however I've learned something important today.

IF you're creating a VM and attaching a disk to it - there is one big difference between VMDK and QCOW disk format.

VMDK disks cannot be resized. QCOW disks can be resized using the proxmox web gui. Option for resize is always present however if you chose VMDK you will not be able to resize the drive.


it will however work with QCOW.

I know I am necroposting however this was the first thread which I've found when searching for "vmdk or qcow proxmox" in google so... I guess its important to add this information here for future users like myself.



Regards.

Andrzej

 

[albgen]

AndrzejL you are right. This is a big limitation and it is not even warned the user when importing or creating a vm with vmdk.​

 

[tom]

AndrzejL you are right. This is a big limitation and it is not even warned the user when importing or creating a vm with vmdk.​

Just read the documentation before you work with Proxmox VE - the part for this topic:

https://pve.proxmox.com/pve-docs/pve-admin-guide.html#chapter_storage

 

[albgen]

yes tom, true, but but you know, reading hundreds of pages is not very simple. Currently i use proxmox for development environments and the reason is exactly this. The learning curves and the suprises

It would be nice to show a warning to the user when he is dealing with the disk of a vm. In case he will select a vmdk, a nice warning saying: There are limitation with this format. We recommend using qcow and/or raw format ...

warned user means saved user(from conversion or other activities)

thanks

 

[tom]

It would be nice to show a warning to the user

Not for the majority of our users. They do not find this nice, they are annoyed by too many warnings.

And this is not a real problem, its just a limitation of the vmdk format with Proxmox VE.

 

[djsami]

VMDK ....

[root@mystifying-jackson ~]# hdparm -Ttv /dev/sda2

/dev/sda2:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
multcount = 0 (off)
readonly = 0 (off)
readahead = 8192 (on)
geometry = 13054/255/63, sectors = 59006943, start = 3907584
Timing cached reads: 12842 MB in 1.99 seconds = 6466.17 MB/sec
Timing buffered disk reads: 172 MB in 3.14 seconds = 54.83 MB/sec
[root@mystifying-jackson ~]#
[root@mystifying-jackson ~]#
[root@mystifying-jackson ~]# hdparm -tv /dev/sda2

/dev/sda2:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
multcount = 0 (off)
readonly = 0 (off)
readahead = 8192 (on)
geometry = 13054/255/63, sectors = 59006943, start = 3907584
Timing buffered disk reads: 348 MB in 3.01 seconds = 115.80 MB/sec



qcow2 ....


[root@mystifying-jackson ~]# hdparm -Ttv /dev/sda2

/dev/sda2:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
multcount = 0 (off)
readonly = 0 (off)
readahead = 8192 (on)
geometry = 13054/255/63, sectors = 59006943, start = 3907584
Timing cached reads: 13566 MB in 1.99 seconds = 6822.36 MB/sec
Timing buffered disk reads: 1486 MB in 3.01 seconds = 494.33 MB/sec
[root@mystifying-jackson ~]# hdparm -tv /dev/sda2

/dev/sda2:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
multcount = 0 (off)
readonly = 0 (off)
readahead = 8192 (on)
geometry = 13054/255/63, sectors = 59006943, start = 3907584
Timing buffered disk reads: 4576 MB in 3.00 seconds = 1525.00 MB/sec


RAW.....


[root@mystifying-jackson ~]# hdparm -Ttv /dev/sda2

/dev/sda2:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
multcount = 0 (off)
readonly = 0 (off)
readahead = 8192 (on)
geometry = 13054/255/63, sectors = 59006943, start = 3907584
Timing cached reads: 12850 MB in 1.99 seconds = 6460.30 MB/sec
Timing buffered disk reads: 1226 MB in 3.01 seconds = 407.91 MB/sec
[root@mystifying-jackson ~]# hdparm -tv /dev/sda2

/dev/sda2:
SG_IO: bad/missing sense data, sb[]: 70 00 05 00 00 00 00 0a 00 00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
multcount = 0 (off)
readonly = 0 (off)
readahead = 8192 (on)
geometry = 13054/255/63, sectors = 59006943, start = 3907584
Timing buffered disk reads: 2472 MB in 3.00 seconds = 823.87 MB/sec
[root@mystifying-jackson ~]#

comment your Samsung nvme SSD