Hi guys
Do anybody have any feedback about CBT support on NFS datastores ?
I just wanna make sure those datastores won't be a stepping stone to
issues.
I could collect some pieces of information here and there but there is a
lot contradictory information on that topic, at least, it seems to me.
I understand, and have already noticied in the past, that during the first
backup all blocks will be stored even if unused. Moreover, I don't care
about thin disk turning into thick upon restoration.
According to B/A Client documentation, CBT feature can be enabled:
https://www.ibm.com/support/knowledgecenter/SSGSG7_7.1.0/com.ibm.itsm.client.doc/r_cmd_bkupvm.html?lang=en
When CBT is enabled, it tracks disk changes when I/O operations are
processed by the ESX or ESXi server storage stack on the following disks:
- A virtual disk stored on VMFS; the disk can be an iSCSI disk, a local
disk, or a disk that is on a SAN.
- A virtual disk stored on NFS.
- An RDM that is in virtual compatibility mode.
Also in this technote, it looks good:
http://www-01.ibm.com/support/docview.wss?uid=swg21681916
For non-VMFS volumes or NFS volumes CBT returns an error or a single
extent covering the entire VMDK. If an error is thrown, the data mover is
forced to create a synthetic extent covering the entire disk. This
scenario means that a thin-provisioned VMDK is converted into a
thick-provisioned VMDK. The previous statement is always true for
thin-provisioned VMDKs on NFS datastores. Also, a thick eager zero
provisioned VMDK returns a single extent covering the entire disk because
all blocks are allocated and zeroed. After the first full backup the data
mover saves the current CBT change ID and uses it to get the incremental
data during the next backup.
Despite a vmware KB states
http://kb.vmware.com/kb/10350
When backing up virtual disk residing on NFS datastores, do not enable
CBT, which is a VMFS only feature.
Cordialement / Best regards,
Christophe COPIN
BP2I SP54C
Projets et Ingénierie des Infrastructures de Sauvegarde
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