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Peter_Genes's avatar
Peter_Genes
Level 3
15 years ago
Solved

difference between vxassist snap & vxsnap

Hi Friends

Can anyone point me to what exactly is difference between taking snapshot via vxassist snap options & vxsnap ?
our environment uses vxsnap though however was interested to know the difference

thanks

Pete

Basics
business continuity
Storage Foundation
  • Gaurav_S's avatar
    Gaurav_S
    15 years ago

    Hi Pete,

    vxassist snapstart/snapshot is traditional way of taking snapshots.... majorly with vxassist you will simply add a plex & data will be copied however it will not contain the updated data (or called point in time copy), so lets say you took the snapshot using vxassist snapstart, whatever data was there at that time gets copied to additional mirror plex, however if data is updated on source volume, there is no track of it. so next time when you are refreshing the snap, whole lot has to be synced again

    To overcome this vxsnap was created, in vxsnap you attach something called as DCO logs to the source volume, these logs keep a track of data blocks changed, so in this technology, once your snapshot is done, DCO logs will start tracking the blocks changed.... When you go for refreshing the snapshot, only changed blocks will be synced... (you can say like differential sync), making operation faster...

    However keep a note, you need a valid license to use these features, If I remember correctly, "fastresync & DGSJ" should be enabled for this.

    you can refer to volume manager admin guide for further explanation on how snapshots work, you can find admin guide here:

    https://vos.symantec.com/documents


    Hope this answers....

    Gaurav
  • Gaurav_S's avatar
    Gaurav_S
    Moderator
    15 years ago

    Hi Pete,

    vxassist snapstart/snapshot is traditional way of taking snapshots.... majorly with vxassist you will simply add a plex & data will be copied however it will not contain the updated data (or called point in time copy), so lets say you took the snapshot using vxassist snapstart, whatever data was there at that time gets copied to additional mirror plex, however if data is updated on source volume, there is no track of it. so next time when you are refreshing the snap, whole lot has to be synced again

    To overcome this vxsnap was created, in vxsnap you attach something called as DCO logs to the source volume, these logs keep a track of data blocks changed, so in this technology, once your snapshot is done, DCO logs will start tracking the blocks changed.... When you go for refreshing the snapshot, only changed blocks will be synced... (you can say like differential sync), making operation faster...

    However keep a note, you need a valid license to use these features, If I remember correctly, "fastresync & DGSJ" should be enabled for this.

    you can refer to volume manager admin guide for further explanation on how snapshots work, you can find admin guide here:

    https://vos.symantec.com/documents


    Hope this answers....

    Gaurav
  • Peter_Genes's avatar
    Peter_Genes
    Level 3
    15 years ago
    Gotcha

    Thanks alot guarav  for explaination, I will still run through admin guide

    one more query, you mentioned vxassist snapstart/snapshot, snapstart is going to start the snapshot ie mirror the plex & snapshot option will disassociate the snap plex & move it to a new volume, is that a fair statememt ?

    ta

    Pete
  • wzis's avatar
    wzis
    Level 3
    15 years ago
    The answer given is not correct. The difference between the 2 types of snapshots:
    For vxassist snapshot: you need to prepare (copy data) first, and wait for the snapstart to finish, and then at the point of the time when you want to take a snapshot of volume data, run "vxassist snapshot" to create it.

    For vxsnap snapshot, you get the snapshot of the volume first, and the real data will be copied over later.

    These 2 types of snapshots will co-exist, and vxassist snapshot won't be replaced by vxsnap snapshot.