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Fast non-volatile storage, such as non-volatile RAM and battery-backed volatile RAM, is widely deployed as the write cache in the storage controller to hide the latency of writes and prevent data loss. Due to the high cost of nonvolatile RAM and the short life of battery, the write cache is always much smaller than the read cache. To extend the size of write cache, we propose a Compressed Write Cache (CWC) in the storage controller using an adaptive compression scheme. Our prototype implementation of CWC and extensive trace-driven evaluation results show that the average user response time reduces by up to 30.1% and the destage count reduces by up to 31.3%. The benchmark experiments show that CWC gets improvement up to 32% in IOPS and 24.2% in average response time while degrades performance by 1.2% in the sequential access case.