Allocated snapshot space exceeded the configured limit

[ValentinSimaN]

Hello,

We have 2 x MSA 2052 that replicates some volumes between them from primary DC to secondary DC.

The problem is that at the time of replication we get the following error on the destination array: allocated snapshot space exceeded the configured limit. When it hits 100% it automatically drops below 75%.  What can cause this issue? I will put some information here about the volumes and other stuff.

# show snapshot-space
Snapshot Space
--------------
Pool: A
Limit (%Pool): 15%
Limit Size: 13.6TB
Allocated (%Pool): 0.0%
Allocated (%Snapshot Space): 0.3%
Allocated Size: 43.1GB
Low Threshold (%Snapshot Space): 75%
Middle Threshold (%Snapshot Space): 90%
High Threshold (%Snapshot Space): 99%
Limit Policy: Notify Only

# show snapshots type all
Pool Name Creation Date/Time Status Status-Reason Parent Volume Base Vol Snaps TreeSnaps Snap-Pool Snap Data Unique Data Shared Data Retention Priority
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
A x_vol.S2 2020-02-13 13:13:03 Available N/A x_vol x_vol 0 4 N/A 19.9TB 8241.8MB 19.9TB never-delete
A x_vol.S1 2020-02-13 13:13:03 Available N/A x_vol x_vol 0 4 N/A 19.9TB 0B 19.9TB never-delete
A x_vol.S3 2020-02-13 13:13:04 Available N/A x_vol x_vol 0 4 N/A 0B 0B 0B never-delete
A y_vol.S2 2022-08-29 11:28:43 Available N/A y_vol y_vol 0 4 N/A 499.9GB 15.1GB 484.7GB never-delete
A y_vol.S1 2022-08-29 11:28:43 Available N/A y_vol y_vol 0 4 N/A 499.9GB 0B 499.9GB never-delete
A y_vol.S3 2022-08-29 11:28:44 Available N/A y_vol y_vol 0 4 N/A 0B 0B 0B never-delete
A z_vol.S2 2022-08-29 11:34:06 Available N/A z_vol z_vol 0 4 N/A 8947.6GB 9.4GB 8938.2GB never-delete
A z_vol.S1 2022-08-29 11:34:06 Available N/A z_vol z_vol 0 4 N/A 8947.6GB 0B 8947.6GB never-delete
A z_vol.S3 2022-08-29 11:34:07 Available N/A z_vol z_vol 0 4 N/A 0B 0B 0B never-delete
A w_vol.S2 2022-08-29 11:36:50 Available N/A w_vol w_vol 0 4 N/A 8950.6GB 10.2GB 8940.3GB never-delete
A w_vol.S1 2022-08-29 11:36:50 Available N/A w_vol w_vol 0 4 N/A 8950.6GB 0B 8950.6GB never-delete
A w_vol.S3 2022-08-29 11:36:50 Available N/A w_vol w_vol 0 4 N/A 0B 0B 0B never-delete

# show replication-snapshot-history
Name Snapshot History Count Snapshot Basename Retention Priority
------------------------------------------------------------------------------------------------
w_replset disabled 1 never-delete
z_replset disabled 1 never-delete
y_replset disabled 1 never-delete
x_replset disabled 0 never-delete
------------------------------------------------------------------------------------------------

Best Regards,

Valentin Sima

[Sahana_S]

Hello @ValentinSimaN ,

As per the output of the command "show snapshot-space", you have set the limit policy to "Notify Only".

There is an another policy as "delete", which means when the snapshot space is reached an event is generated and logged and automatic deletion of snapshots occurs.

You can also increase the limit percent-of-pool. 

For example, # set snapshot-space pool A limit 20% limit-policy delete

Also, the snapshot retention priority has been set to never-delete. You may choose the below options based on the priority:
1. never-delete: Snapshots will never be deleted.
2. high: Snapshots may be deleted after all eligible medium-priority snapshots have been deleted.
3. medium: Snapshots may be deleted after all eligible low-priority snapshots have been deleted.
4. low: Snapshots may be deleted.

Hope this helps!

Thanks,
Sahana S

[ValentinSimaN]

Hello @Sahana_S ,

Thank you very much for your answer. What I wanted to understand is why are the internal snapshots during the replication is that big? Because the delta for sure is not in TB, I think that it is in GB.

Best Regards,

Valentin

[Sahana_S]

Hello @ValentinSimaN ,

When first created from the primary volume, the internal snapshots consume very little space but will grow as data is written to the volume.
Just as with any virtual snapshot, the amount of disk space used by an internal snapshot depends on the difference in the number of shared and unique pages between itself and the volume.
Even though the internal snapshots are hidden from the user, they do consume snapshot space (and thus pool space) from the virtual pool.

If the internal snapshots are larger than anticipated and take up a lot of snapshot space, you can adjust the snapshot space thresholds or increase the snapshot space to prevent unintentional automatic deletion of snapshots that you want to retain.
To monitor the snapshot space for virtual pools, use the "show snapshot-space" CLI command.
To monitor the size of the internal snapshots, use the "show snapshots" CLI command with its type parameter set to replication.

If you feel this was helpful, please click the KUDOS thumb below. Also consider marking this as an "Accepted Solution", if the post has helped to solve your issue.

Thanks,
Sahana S

[support_s]

Hello,

Let us know if you were able to resolve the issue.

If you are satisfied with the answers then kindly click the "Accept As Solution" button for the most helpful response so that it is beneficial to all community members.

Please click on "Thumbs Up/Kudo" icon to give a "Kudo".

[ValentinSimaN]

Hello @Sahana_S ,

What I wanted to point out is that if I start a replication for one volume, even if the delta is very small, the destination array still generates alerts. If let say that snapshot space is reached, wouldn't the source MSA send alerts also? Because, as far I understood, the snapshots are done first on the source sice and then on the destination side. That will result in having the threshold reached on both source and destination, correct?

BR,

Valentin