MSDP thresholds best practices

[Technic_rus]

Hi All!

We have two NBU 7.6.0.4 servers with MSDP. Each server has 14TB attached. I noticed that 1.4TB are reservered. Please see crcontrol --dsstat:

D:\Program Files\Veritas\pdde>crcontrol --dsstat

************ Data Store statistics ************
Data storage      Raw    Size   Used   Avail  Use%
                  14.0T  12.6T  10.2T   2.4T  81%

Number of containers             : 84821
Average container size           : 130942704 bytes (124.88MB)
Space allocated for containers   : 11106691158478 bytes (10.10TB)
Reserved space                   : 1540376379392 bytes (1.40TB)
Reserved space percentage        : 10.0%

Use "--dsstat 1" to get more accurate statistics

This reserve is controled by LowSpaceThreshold variable from contentrouter.cfg:

; If the free disk space falls below the low space threshold on the storage,
; queue and/or database partitions, the CR will no longer permit store tasks
; to add new data to the CR and will issue an error to the SPA.
; A value higher than the WarningSpaceThreshold will be treated as equal to
; the WarningSpaceThreshold.
; The default value is 10%. Value 0 disables this threshold (NOT recommended).
; Possible suffixes are:
; b, Kib (1024), Mib, Gib, Tib, Pib, Eib, Kb (1000), Mb, Gb, Tb, Pb, Eb, %.
; @restart
LowSpaceThreshold=10%

I think that 1.4TB reserve is redundant.

Could you please advise what is the best practice here? Can I safely decrease it to e.g.3% ?

Thank you in advance.

[Nicolai · Accepted solution]

Please remember that free space is required for the MSDP house keeping. MSDP does not work as a normal disk where deletion of a file immediately free space. 

I am almost certain lowering the value to 3% will cause serious issues - no space of MSDP house keeping.

I would be rather conservative with changing default values.

[Technic_rus]

Hi Nicolai.

We have short queues. CRQP usually takes few minutes to complete.

I don't think that CRQP could utilize huge amount of space.

[Big_Phil]

Hi, 

MSDP has itself's database and other meta data.

I even decreased it to 5%, but backup job failed with data checksum error.

After resume it to 10%, backup job can run successfully.

[Nicolai]

Its your system, but I wouldn't change the values unless support has given me a OK. 

If you do change the value - decrements it with 1% steps. 

[Technic_rus]

I raised support case. I will provide an update here once I have reply.

[Nicolai]

Please do.

[Technic_rus]

Symantec confirmed that in 7.6 version default threshold is 4% but recommends to keep 10%:

 Our recommendation would be to leave your current LowSpaceThreshold value at 10% to allow for the best NetBackup database performance, and add additional storage if required.

[Nicolai]

Thanks for updating this thread with Veritas recommendation.

By the way: MSDP in 7.6 is about 30% faster than 7.5 on same hardware.