Re: Raw vs. Cooked files

A lotta years ago, when I was an Informix consultant, I was sent to solve a problem at some isurance company. The system would periodically freeze up while the monitors showed frenzied activity. To cut to the chase (out of character for me, I know :-) the problem turned out to be that the symbolic links for all the chunks were actually referencing the cooked disks - the block device. Every time the Informix system performed a checkpoint, it would choke to 2MB Unix cache as it tried to flush the 100MB+ worth of buffers to the disk. The problem went away after they restored to raw disk devices. The moral, as I see it, is that raw disk is better. for checkpoints. But suppose you had a Unix cache as large as the Informix buffer pool: The checkpoint would be fast because it's all going to other memory. But it won't be out on the physical disk if you crash 2 minutes after the checkpoint. Having the file system set to flush buffer cache after every write may make it more reliable but will slow it down. And it won't be on disk all that reliably either. Stick to raw disk and you will get better performance in checkpoints as well as more reliable recovery. -- Jacob Salomon