At 10:39 6/16/2004, Alan Horn wrote:
Raid 1 is mirroring only. For data integrity reasons I can't see how they could read from any but the master mirror.
WAG alert:
Once the two disks are synchronized, it sounds perfectly reasonable to writes to take the same amount of time (since all data has to be written to both drives), but for reads to be significantly faster by reading from both spindles. There really is no "master" in an equal set of two, I think. Both contain identical data, so you should be able to read from both. I think.
The Linux kernel does give you the ability to read simultaneously from both drives in a Linux mirror array.
By the way, the Promise cards *are* software RAID... all the real RAID computations are done by the driver using the computer's resources. The trick is that the binary driver for Linux is probably less mature and less flexible than Linux native software RAID, so I've always used Promise and HighPoint controllers simply as additional EIDE/ATA controllers and used Linux software RAID. Excellent results. Note that Linux software RAID is also capable of RAID-5, IIRC, which the Promise drivers are not.
Heh, exactly the same reason here. Any Promise installation we had was for ATA100 support.
If you have the budget, I'd strongly recommend the 3Ware cards. Real hardware RAID, native Linux kernel support since 2.2.x, fast, very reliable, and not expensive.
Some gotchas:
3ware RAID 5 sucks and especially when in degraded mode (and this goes for a lot of other hardware RAID cards) because the onboard processor is not fast enough to handle the calculations. Hint: If you see an Intel 960 processor on your RAID board, forget RAID 5.
Linux RAID 5 will be much faster so forget the 3ware RAID card if you want to do RAID 5.
3ware RAID 1+0 also sucks. You are better off configuring two mirrors and using the Linux kernel to achieve the RAID 0 part. This means that, depending on what you got (4 port/8 port/12 port), you will need other disks on the IDE channels for the system if there is nothing left for the system.
