EMC vs. ordinary RAID 5

Hi all, just because some guys of this wonderfull NG told us that we should avoid RAID 5: Here's the result of an I/O throughput comparison unfortunately made on two different platforms: On an EMC with 2TB disk space, 2GB cache connected via 1 x FDDI 100MByte to a HP box I got a maximum of 70MB/sec throughput ( used raw devices with 64KB block size ). Read 1GB, possibly cached by the controller. I read the data 4 x 6 striped disks, each disk was additionally mirrored ( 48 disks ). On a DELL box with a DELL RAID 5 System ( 170GB disk space on 6 disks 64MB cache ) I got a throughput of 65MB/sec ( used block devices ( 2KB blocksize ) on a RedHat Linux Sytem ). The read operations read 700MB of data ( couldn't be cached by the controller ). On both platforms I started several processes to get the best throughput. 8 processes on the HP-box ( 8 CPUs ). 6 processes on the DELL machine ( 2 CPUs ). For all these tests I used the "dd" command for the I/O operations and "time" to measure the real time. On both systems I loaded a 60GB databases. Because I got some troubles with PDQ on the Linux server, I had to disable it during the index built, but overall it took less time to load the database on the Linux Server. So, please let me know why we should not use RAID 5 systems. I/O settings for the IDS: Because I got the best throughput with 6 processes, I must force the Informix engine to use 6 I/O processes. NUMAIOVPS should be set to at least 6, better would be 7-8 for regular OLTP environments. ( No raw device support on Linux ). Fragmentation strategies: Informix determines the number of scan threads for a sequential scan operation on a single table on the number of table-fragments. Each table-fragment must reside on a different dbspace, therefore you will need 6 dbspaces. By using an expression based fragmentation strategy you can reduce the disk I/O ( the speedup depends on the size of the fragments which can be excluded by the optimizer ). Any comments ? Stefan Phone: +49 89/3565478-2 --------------- --- Fax: +49 89/3565478-3 ------------- ------ mailto:/stefan@weideneder.de --- -------- http://www.weideneder.de -----