Disk space required for snapshot process

[rufusleonard]

I was wondering if someone could help me understand volume sizing and snapshot sizing

I have a drive I want to snapshot.

The drive on the server is 1GB and I want to store 5 snapshots

There is a 1GB file on the drive and the file content changes 100% every day but never goes larger than 1GB

How large does the volume have to be?

Do I need to have 7GB volume in total

 1GB for the data portion drive

 + 5GB (5x 1GB) for the 5 snapshots

 + 1GB for the snapshot process - i.e. the space required to take the snap before saving it?  

or do I only need a 6GB volume

1GB for the data portion and 5GB for the 5 snapshots

Any help would be appreciated

[SpindleNinja · Accepted solution]

Snapshots are block level.   So... technically yeah,  if 100% of the blocks are changed between snapshots.  you'll need to account for 100% of the blocks.  

No space is "required to take the snapshot" 

Though, I would do the 7GB thin volume to give yourself some breathing room.    so 1.5G for the file space and 5.5 for the snapshot space.   The snapshot % is adjustable anytime,  so you can fiddle with it after the fact if you want too.  

[aborzenkov]

---

@SpindleNinja wrote:

No space is "required to take the snapshot" 

---

There is some overhead for copying metadata, so it is not entirely free. But this sounds like exam question in which case answer is likely 6 🙂

[SpindleNinja]

There have been questions posted in the community that I've used as ideas for senario questions in the exams i've helped write.   😉  

But yes. 

[rufusleonard]

Thanks for the help

[FelixZhou]

when you take a snapshot, no space will be taken immediately. when changes come in to the original data blocks, the original blocks will be moved to the snapshot area. if your data is 1GB, the snapshot  will hold all changed blocks until next snapshot. 

volume can be expanded anytime as you need, you can give 2GB to start, if not enough, expand the size. if thin provisioning is being used, you will not waste any space.

[aborzenkov]

---

@FelixZhou wrote:

the original blocks will be moved to the snapshot area

---

Original blocks are not moved anywhere on WAFL nor is there any "snapshot area". You confuse WAFL with traditional Copy-on-Write snapshot implementation.

[FelixZhou]

Thanks for clarify.

Fei Zhou
Data Protection Lead, Systems Architecture
Catholic Health Services of Long Island
245 Old Country Road
Melville, NY 11747
Phone: 631-465-1523
fei.zhou@chsli.org

[cid:image001.jpg@01D2F71D.BF4184A0]