Multiple sessions are fine. I regularly pause one long-running session to do a quick shorter session. You will want to use the --session parameter to give additional ones different names.
Multiple sessions actively running at the same time will compete for resources, unless you target specific devices (CPU for one and GPU for the other, or distribute to specific GPUs, etc.)
Multiple sessions actively running at the same time will compete for resources, unless you target specific devices (CPU for one and GPU for the other, or distribute to specific GPUs, etc.)
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