Brief explanation of the memory consumption of LiteSpeed, in particular, possible contention with the resources for SQL Server.
VDI uses the area set by the SQL Server mem to leave setting. When SQL Server starts up it allocates mem-to-leave amount of memory. It then allocates its buffer pool and a number of other memory allocations needed for the database to run. Then when it is finished allocating all of the memory required at the end of start up it then *releases*/frees the memory it had just allocated for the MemtoLeave. It does this in this manner so that it will have a contiguous MemtoLeave area separate from the buffer pool.
One can see this behavior by injecting into sqlservr.exe and detouring malloc. THEN as third party apps execute extended stored procedures or connect and use VDI to perform backups, any memory that SQL Server allocates just using normal malloc or AllocateVirtualMemory will be taklen from the MemtoLeave area. SQL Server native backups do not use VDI and do not allocate extra memory from that area when doing native backups.
To estimate the required resources:
Buffer Count * Max Transfer Size * # VDI Threads.
For example the default for a quad-CPU machine is three threads:
20 (Buffer Count) * 1048576 (Max Transfer Size) * 3 (VDI Threads) = 61MB or about 20MB
