Re: Informix mirroring [6769]

<Also posted to IIUG Forum> OH I CAN'T RESIST! Informix mirroring OVER RAID5? Do you have a death wish? NO RAID5!!! NO RAID5!!! NO RAID5!!! NO RAID5!!! NO RAID5!!! NO RAID5!!! This is bad on SO many levels. OK, first issue, if you ARE using Informix mirroring, the only one side of the mirror will have been trashed when the array crashed. You should only have to tell IDS to recover the failed mirror from the remaining member by dropping either the primary or the mirror chunk(s) (whichever one failed) and then adding back the replacement mirror segment(s) using onspaces. If you have both sides of the mirror on the same failed array, well that's just foolish and you deserve to lose your data. (Not to be cruel, but ...) Finally, you should not be mirroring over RAID5. RAID5 is inherently UNSAFE AT ANY SPEED, besides being slow, and adding mirroring just adds overhead without much additional safety. The RAID5 underneath is undermining the safety of the mirror. If you want to mirror but also want the additional performance of a stripe, then either mirror at the Informix level from RAID0 (stripe only) arrays (which amounts to a RAID01 array in practice), or better yet, set up an OS or VM level RAID10 array and do away with the Informix mirroring. The RAID10 array will tend to be about 10% faster than Informix mirroring of RAID0 arrays, much faster to recover from a down drive, and less likely to lose all of your data. Your RAID provider is reporting an error back to Informix even though the data is being reconstructed using the (a common RAID5 implementation problem) and that is why IDS perceived the logical partition to be 'down'. I've seen this often with RAID5 and NEVER with RAID1 or RAID10. PLEASE PLEASE read my paper on the subject of "Why should I not use RAID5?" at: http://www.baarf.com/RAID5_versus_RAID10.txt as well as the other postings on the BAARF site (www.baarf.com). Oh, and remeber: NO RAID5!!! NO RAID5!!! NO RAID5!!! NO RAID5!!! NO RAID5!!! NO RAID5!!! Art S. Kagel ----- Original Message ----- From: Chris Salch <ids@iiug.org> At: 5/19 12:12:33 We have an Informix 7.31.UD6 database running on HPUX 11.11i. For various reasons, the parituclar machine that this database runs on has had quit a few issues with failing hard drives. Our database use software raid for some HPUX volumes and Informix mirroring for the database. In about half the cases where a drive has failed, we've had to reload the database from tape even if the HPUX volumes recover without reloading from tape backup. On the most recent occasion, the a drive was discovered to be failing and replaced prior to complete failure. Again, the HPUX volumes on the failing drive recovered readily and the operating system came up nicely. Unfortunately, the database was not so lucky, it had to be restored from a tape backup. To replace the drive, we shut the database engine down and then took the machine down completely. An hp technician replaced the failing hard drive and used various vg commands to restore logical volumes and data to the new drive. (note: There was no HPUX mirroring of the Informix database, all chunks were mirrored through the datbase engine.) It was assumed that since none of the chunks were marked as down, the database should come up and restore any missing data from the good drive. As mentioned before, this was not the case. Is there anything that should be done to tell Informix that a drive has been replaced? The only thing I can come up with is that the engine saw a blank drive where it expected data and freaked. Should the questionable chunks be taken offline before replacing a failing drive that has not totally died? Any input is appreciated. Chris Salch ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.