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Question on snapshots at DR site - RP with XIO
Hello,
When the CG is configured, I see RP creating 3 snaps on XIO at the DR site. The first snap is a readonly snap named like VolumeXXX6, and then like 4 seconds later 2 snapshots are taken simultaneously, one named with suffix _SMP, and the other named like VolumeXXX7. One of these newly taken snaps (Volume XXX7) is readonly as well, and all the new writes during initial synchronizarion are being written to the snap with suffix _SMP. What is the purpose of those readonly snaps (VolumeXXX6 and VolumeXXX7)? Also, do we see 3 snapshots being taken all the time at the DR copy, instead of one?
forshr
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June 24th, 2016 07:00
The SMP device is a pseudo device for the snapshot and assumes the SCSI personality of the snapshot that is being created. Thus VolumeXXX7 is created from the SMP device hence why you see the writes going to the SMP device and why the SMP device and VolumeXXX7 are created simultaneously. This next replication will show the SMP device linked to snapshot VolumeXXX8.
Regards,
Rich Forshaw
Consultant Corporate Systems Engineer - RecoverPoint & VPLEX (EMEA)
Data Protection and Availability Solutions
EMC Europe Limited
Mobile: +44 (0) 7730 781169
E-mail: richard.forshaw@emc.com
Twitter: @rw4shaw
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forshr
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June 22nd, 2016 09:00
Hi Cherry,
The first snap, VolumeXXX6 is an empty snap (a dummy if you like) that is used to create the first diff snap, VolumeXXX7, as part of the initialization process. The SMP (Snapshot Mount Point) acts as the SCSI identifier for the device hence why the writes are written to it.
Regards,
Rich Forshaw
Consultant Corporate Systems Engineer - RecoverPoint & VPLEX (EMEA)
Data Protection and Availability Solutions
EMC Europe Limited
Mobile: +44 (0) 7730 781169
E-mail: richard.forshaw@emc.com
Twitter: @rw4shaw
EMC Europe Limited
Registered in England with Company No. 00990752 Registered office address: Level 1, Exchange House, Primrose Street, London C2A 2EG
The information contained in this e-mail message and any files transmitted with it are confidential. It is intended only for the addressee and others authorised to receive it. If you are not the intended recipient or the person responsible for delivering the message to the intended recipient, you are advised that you have received the e-mail in error; please delete it and notify the sender immediately. You should not retain the message or disclose its contents to anyone. Any disclosure, copying, distribution or action taken in reliance on the contents of the e-mail and its attachments is strictly prohibited.
Cherry251
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June 23rd, 2016 13:00
Rich,
Could you please clarify on this statement:
"The first snap, VolumeXXX6 is an empty snap (a dummy if you like) that is used to create the first diff snap, VolumeXXX7."
But, when I look at the snapshot tree, it is like follows:
Copy Volume (Root)
VolumeXXX6 (First read only snap)
SMP (The one with suffix SMP, to which the writes take place. Second snap)
VolumeXXX7 (Third snap which is readonly. This one and the SMP snap almost got created simultaneously)
Looking at the snapshot tree, it is clear that the snap VolumeXXX7 is created from the SMP snap, not from VolumeXXX6.