Re: Urgent!! Question about add a chunk

All of the respondents are correct that the main problem with using the Block or COOKED device rather than the Character or RAW device is performance. However, the old adage that using the COOKED devices is not SAFE because Informix cannot be sure that the OS Buffer Cache has been synced to disk is an Old Wive's Tale. According to tech support Informix opens all cooked devices and files in O_SYNC mode which means that while I/Os still do go through the OS buffer cache they are indeed flushed and synced out to disk immediately and synchronously so that when the write() system call returns to the AIO VP with a success code the data is safely on disk. Unfortuneately this is 15-25% SLOWER than writing to COOKED files/devices without O_SYNC which is in turn 10-15% slower that writing to RAW devices. You get the picture. In general, writing to a COOKED device is 25%-40% slower than RAW devices and reads are similarly effected (10-15% slower) because of the overhead of copying the data into the OS buffer cache, before copying it again into the Informix buffer pool, from whence it will almost never be reread because of the Informix buffer pool. Art S. Kagel