Re: Safe, efficient space allocation for mirrored DB - two drives.

Don Miller wrote: > Database will have two "working" chunks, plus two mirror chunks (one for > each of the "working" ones; each chunk will be ~2GB). The first drive > will have the first "working" chunk, and the mirror of the second; the > second drive will have the second "working" chunk, and the mirror of the > first. > The correct terminology is "primary" and "mirror" chunks. In the case of Online, they are both "working" chunks, i.e., you will find both the primary and the mirror to be used when working with the data. This is one of the advantages of implementing mirroring in Online, you will get putative increased throughput on selects because you are reading over twice the number of drives. As far as putting on one drive a primary of one chunk and the mirror of another, there is no reason that I can think of to do this. As far as Online goes, these are virtually the same. For less confusion, I put all my primaries on one drive and mirrors on another drive. This will cause less confusion when you are tracing symbolic links to drives. Otherwise, you may incur a criss-cross of file links which can be hard to follow. > As far as I can figure (being a relative Informix novice - I usually do > hardware and software stuff in unix is my "home turf"), that would be the > most efficient allocation; it'd allow simultaneous access on both drives, > and still keep an entire copy of the database on each drive, in case one > failed, it's mirror on the other would be available. > > I'm interested in the group's opinions of this - are there better ways to > set this up, given this size and number of disks, and I'm also curious > as to the operation of mirroring: will the mirror chunk automatically be > available, should the primary one fail? And, should I allocate the space > on the drives the same (primary chunk first), or does it matter? > > The mirror will be automatically available if the primary fails, and the reverse will be true as well. You will either have to set up the mirror chunk at the same time as the primary, or after the primary is set up. -- * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ADDRESS ALTERED TO FOIL SPAMMERS: Remove "*NO-SPAM*" to reply. Cosmo Lee Multi-User Computer Systems Brooklyn, NY "JUST SAY 'NO' TO SPAM" * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *