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DD Test Confusion
Ok, so currently testing some code on a dedicated server I have,
Can anyone explain this to me?
[root@testserver ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
1073741824 bytes (1.1 GB) copied, 9.48912 s, 113 MB/s
[root@testserver ~]# vzctl enter 10
[root@test ~]# dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
1073741824 bytes (1.1 GB) copied, 1.09157 s, 984 MB/s
In the VM I am getting 1GB/s IO, does OpenVZ now cache to ram? Its been a while since ive setup a openvz based server.
Comments
ploop ploop ploppety ploop..... ploop
Downsides of ploop vs simfs?
its new, bugs do strike from time to time, aside from that, none.
Hmm, im assuming with ploop if data block is all zeroes, it is not written to the disk as it was with simfs
bugs such as? what's the impact then?
take a look at the bug tracker, to many to talk about and list on LET
Ploop is thin provisioned storage but if you use a byte and then delete it, the byte is still used according to OpenVZ.
Example: If you have an OpenVZ VPS with 10GB of storage, you download 5GB, then delete 3GB, the host node shows 5GB used until you compact it (might not reclaim all 3GB though and is a very long process for large VPSs).
Downside of ploop is total data loss is very easy to experience so keep good backups. Plenty of threads on vpsBoard going into detail about how little it takes for ploop files to become corrupt and requiring a completely new VPS build and how the "repair" tools either won't work or will make it worse. If you need to fsck the filesystem, you're S.O.L. and better off restoring from a backup. I'm not going to say that data loss from ploop is common, but it happens more often than a drive failure from what I've seen and if your server reboots unexpectedly, it's time to pull your backups out.
EDIT: Here are some fun reads that should convince you to keep good backups of ploop VPSs...
https://vpsboard.com/topic/6641-ovz-error-in-ploop-fname-cmp-during-ct-restore-fs-with-other-cts/
https://vpsboard.com/topic/4277-heads-up-openvz-updates-will-probably-break-your-system/page-4#entry87768
https://bugzilla.openvz.org/show_bug.cgi?id=3030
https://vpsboard.com/topic/4277-heads-up-openvz-updates-will-probably-break-your-system/page-2#entry72778
https://vpsboard.com/topic/4277-heads-up-openvz-updates-will-probably-break-your-system/page-3#entry76893
Wow, ploop really looks like a no-go right now. Maybe in the future but thinking I will stay away from it in the meantime.
Not to mention that DD test is quite useless
.
Not when it identified that issue for him.