Re: Informix on RAID-5

Michael E Willett wrote: > > Koen.VanderElst@ping.be (Koen Van der Elst) writes: > > >>I disagree! We are currently using RAID-5 with 60 GB hard disk from Sun and two of such servers are in > >>production since June 3rd. There are many other servers which are not in production yet. So I will > >>only address the two servers that are in production. > >> > >>We did not do fragmentation at all. Yet we have about 40 temps, two shifts. We are considering to add > >>another shift. The performance monitoring tool we used (SymBEL) complaint a lot about CPU overload, > >>slow internal hard disk. But it never complaint about the disk array. > > >RAID 5 will slow down your write-to-disk times on most Disk Arrays or > >Logical Volume systems. <snip> I'm glad that you have acceptable performance in your RAID 5 environment. Certainly RAID 3 or 5 provide good redundancy and recoverability. However, they are generally not thought of as a performance enhancer. A database manager cannot access a RAID 3 or 5 disk array any faster than it can access a single disk drive. Since these disk arrays can typically handle large amounts of data, they usually turn into bottlenecks on a database system. A DBMS might end up with their entire data environment sitting on one disk array, which essentially means all data is going through the same bandwidth as if you were using just one disk. For very large database environments where money is not a big issue, you should get OK performance with RAID 3 or 5 if you can have many disk arrays implemented as if they were one logical disk, i.e. one array for data, one array for indexes, etc. RAID 1 seems to be a very well-accepted and even recommended RAID solution for database environments. This mode is basically just a hardware mirror of an entire disk to another disk. It is very important that the disk cache be configured for "write" in RAID environments. This will counteract the overhead of the extra writes. > They've engineered those performance problems out with the RAID 7 > level. > <snip> Great! Can you supply more info? Brenda Reed