Block size recommendation for SQL Server 2014 Standard backup LUN

Question

I'm setting up a new SQL Server cluster, so my database storage is on a SAN. I'm on SQL Server 2014 Standard on Windows Server 2012R2. I have the block size for the data, log and tempdb LUNs set to 64k, per the recommendation in Brent Ozar's SQL Server Setup Checklist. My question: what should the block size be for my backup LUN?

Answer 1

I'm setting up a new SQL Server cluster, so my database storage is on a SAN

Ah, no. Non sequitur - one does not follow the other. You set up a new SQL Server cluster. Your database storage is on SAN. There is no intrinsic requirement for this. In fact, for quite some time AOAG (Always On Availability Groups) with non shared storage are preferred for uptime reasons. Also performance - it is quire hard to get a multi gigabyte per second SAN LUN up (among other things because fiber is 8 gigaBIT - 800megabit raw). It is trivial to do so in a small server with a high performance SSD.

I have the block size for the data, log and tempdb LUNs set to 64k, per the recommendation in Brent Ozar's SQL Server Setup Checklist.

THat makes IMHO no sense and runs counter anything I ever experienced. SQL Server stores in 64kb extends - but it always tries to write and read multiple. 256kb to 512kb look better, ESPECIALLY with the caching that a proper IO subsystem does. Theoretically 64kb makes sure you never have split IO - practically this makes little sense, particularly on a SAN with gigabytes of cache.

My question: what should the block size be for my backup LUN?

Whatever you like. You give us little information how you make backups (or do you not have an enterprise backup tool?) Generally backups are a lot less problematic from IO than the active data store. There is, for example, very little random IO on them.