G
gus bjorklund
Guest
> > Does anyone have a simple, concise argument against RAID5 for Progress, suitable for use against non-technical management and a "this is how we've always done it" mentality? This is RHEL 7, but I doubt that matters... > Short answer: RAID 5 costs you more. Slightly longer answer: It will cost you a lot more moeny in the long run and at times when you can least afford it. This is so because inherent in the design of RAID 5, RAID 6, RAID DP, etc (all variants of the same design) is the fact that writing to disk is slower with RAID 5 etc than it is with other array architectures like RAID 10. Salesmen will claim this is mitigated by having large caches. That helps but will not solve the problem. For example, let's say you have a RAID 5 setup with 3 disk drives (the minimum required). When a disk block is written to the array, it must be written to two separate places - once to a disk block that has the data and then a "parity block" used for recovery purposes must also be written. Sometimes but not always, the data on the other drive has to be read in order to compute the parity block. With RAID 6, there are two parity blocks. So the 3 disk array (or 4 if RAID 6) has the same or less write thruput than a single disk drive. Simply put, what all this means is that writing can be slow, especially when doing some bulk maintenance operation like restoring a backup after a crash, dumping and loading, reseeding a replication target, or index rebuilds. All those operation will take longer than they need to and that will result in increased unplanned downtime when doing disaster recovery. Increasing unplanned downtime costs money. The cost of the increased downtime can easily surpass the cost of a decent disk setup. =
Continue reading...
Continue reading...