Shared memory

[JonThompson]

So I've read up on shared memory and how it plays into bakbone. In fact, they have an article detailing how to change it in Leopard, although it appears to be unlinkable. The guys at 318 also posted an article explaining what each variable is and what to change it to for different settings:

http://www.318.com/techjournal/?p=162

My question is this: What ratio should I bump up to? My NetVault/everything else server has 4GB of RAM in it. Am I safe with 512?

I've looked at my memory usage in Activity Monitor, and it appears that my physical memory is full, although my suspicion is that OSXS will always take all available memory and use it.

I've never had issues with memory on the machine, but think that the increasing the shared setting will decrease my backup time.

Oh, and I realize that upgrading my server memory is dirt cheap. (8GB for $260) However, I doubt I will get even that pushed through.

[matx]

When I built a new backup server for Netvault on a 8-core intel Xserve with 4GB of RAM I boosted up the shared memory as prescribed in the Bakbone technote for Leopard, but I am not sure it helped all that much. Increasing the memory/cache settings of the drives themselves (dual LTO-4) in the tape library helped enormously, and using a VTL (virtual tape library) as a staging ground helped the most. Backing up large files (QT, R3D, etc) could feed my LTO-4 tape drive at about 150MB/sec for short bursts, but backing up smaller files was 10X slower. Using the VTL for all backups allows the tape to run at max backup speed. But back to memory settings, is there an advantage to tweaking those shared memory settings above the recommended 512MB stated in the technote? I'm not sure, test some backups before you make the change and after.

[abstractrude]

matx, what are you settings for your FC drives? drive cache?

[matx]

[318Tim]

Bakbone recommends the following drive transfer buffer settings:
Shared memory is allocated in 32Kb blocks. The default of 257, which is the minimum shared memory size, is equal to 8 buffers of 32 Kb plus one Kb.. Therefore, the formula used to determine a valid setting for this field is as follows:
(<Total number of buffers> x 32Kb) + 1 byte

Examples of the optimal values, in KB, that can be specified for some of the drives are given here:

Fast Modern Tape Drives (e.g., LTO (1, 2 or 3), SDLT or SAIT)
65537 (64 MB + 1 KB)

Medium Tape Drives (e.g., DLT8000, DLT7000 and AIT-3)
32769 (32 MB + 1 KB)

Older Professional Tape Drives (e.g., DLT2000, DLT4000, AIT-2, etc.)
16385 (16 MB + 1 KB)

Older Low Capacity Low-end Drives (e.g., EXB-8505, AIT-1, DAT, etc.)
8193 (8 MB + 1 KB)