Saturday, May 31, 2008

Mixing SATA dos and donts

Another day, another bug seemingly hit. I've known for some time that mixing SATA-I and SATA-II devices on the same controller with regards to OpenSolaris seems to be unwise. I've already had systems with the initial ZFS-boot drive being a small capacity and thus likely SATA-I, but the data volumes were SATA-II. My recent issues with the iRAM could be related to having a SATA-I device after a SATA-II drive in the chain, but nothing has been concrete.

However, today I discovered something else. One array I have is made up of all SATA-I drives and was used by a SATA-I RAID card that went south. I happily replaced it with the Marvell SATA-II JBOD card, and it was working just fine. I then lost the 6th of 7 drives, and went back to the manufacturer to try and buy a replacement. Sadly, these Raid Edition drives have been "updated" to be at a minimum of SATA-II for the same model. Replacing the failed SATA-I with the SATA-II worked, but on subsequent reboots, the 7th drive tended to not be enumerated by the Marvell card at startup, and even after re-inserting it, a "cfgadm" was necessary to activate it. Even then, a "zpool import" or "format" to introspect the now configured drive would wedge and never complete the command. Weird, right?

The solution to return to stability was to swap the 6th and 7th drive, so that the SATA-II disk came after all the SATA-I devices in the chain. I'm not sure why it works, but every reboot works now, it never fails to enumerate that last drive and there is no need to manually cfgadm configure the drive post boot. Therefore, a set of truisms are starting to come together with mixed SATA drives. Whether Marvell, Sil3124, or the like, its never a good idea to mix SATA-I and SATA-II devices on a single controller, but if necessary, make sure that the SATA-II drives come after the SATA-I drives. The best configuration is to restrict SATA-I boot devices, such as small 5400 "laptop" drives to their own onboard SATA interface, and leave all SATA-II devices to add-on boards.

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