Techniques for processing I/O operations includes: determining whether a current amount of unused physical storage is greater than a threshold; and responsive to determining the current amount of unused physical storage is greater than the threshold, performing normal write processing, and otherwise performing alternative write processing. The alternative write processing includes: initializing a counter; determining whether a physical storage allocation is needed or potentially needed for a write I/O operation; responsive to determining that no physical storage allocation is needed for the write I/O operation, performing the normal write processing. Responsive to determining that a physical storage allocation is needed or potentially needed for the write I/O operation, determining a first amount of one or more credits needed to service the write I/O operation; and responsive to determining the counter does not include at least the first amount of one or more credits, failing the write I/O operation.