On 25 Jan 2010, at 15:28, Hank wrote: > ... > I have a PE R610 with 2x73GB drives and 4x146GB drives. I'm > thinking of setting up the 2x73 drives as RAID 1, and 3 of the 146 GB > drives as RAID 5. The remaining 146GB drive as a global hotspare.
This is sound. > In this case, if one of the 73GB drives fails, I'm assuming the > controller can use the 146GB drive as a hotspare - Yes. > - but then what > would the procedure be to replace the failed 73GB drive with another, > rebuild the RAID 1 volume, and then return the 146GB back to global > hotspare status? When the replacement 73GB drive arrives, you would use the management software to remove the 146GB from the RAID 1 array, and then add the replacement 73GB to it instead. You can indeed then set the 146GB back to hotspare. I am not familiar with the R610's RAID card or it's software. The normal way to do this, using Dell hardware, would probably be through the Open Manage web interface. But whatever the software you use, this procedure would be absolutely standard for any hardware RAID card. > Or would I be better off just replacing the failed 73GB drive with > another 146gb, and just set it to hotspare status? Depends how paranoid you are. The RAID 1 has two drives. When one fails, you are dependent for some time on the remaining one whilst the hotspare is imaged to match up with it. Likewise when you remove the hotspare and replace it with another. During these periods there's a very (very, very) small risk that the single working drive of the mirror will fail and you'll be hosed. Considering that a drive might fail on average every few years, the risk is very small over the few hours that the procedure takes. If you shutdown the system before physically removing the 146GB, then you should be able to use that as a "backup". The system will boot and the RAID software will show the original 73GB as present and the RAID1 as degraded. You can then plug in the new 73GB and add it to the array (or mark it as hotspare and it'll be added automatically). If anything goes wrong, you can shutdown again and you *should* be able to likewise use the removed 146GB as a degraded RAID1; I don't know for sure if this works with all RAID card, but it seems to on the 3ware I have here. Alternatively you might, for instance, boot from a Live CD and, whilst the array spans the 76gb and the 146gb drives, take an image of it to an external drive or something using (say) `dd`. That's another backup approach. Realistically, I suspect operator error is a more likely risk of catastrophic failure when undertaking drive swaps in RAID arrays. You have a bunch of identical drives and flashing lights, it's easy to get confused. I am always either incredibly nervous when doing stuff like this, or just somewhat flustered at myself afterwards for being too blasé. Even with the option in the software to blink the drive's LED to show which one it is, I am always paranoid I clicked on the wrong drive to blink, and go back to check a couple of times. Best practices would probably be to do as you suggest. Always have a hotspare at least as large as the largest drive in the system, never deliberately remove a drive from a working array. RAID6 is nicer than RAID5, if your controller supports it. A card that would do RAID 1 over 3 drives would be lovely, but I don't know if any do support this. One wouldn't normally use that in everyday use, but in your situation it would allow the replacement 73GB to be added to the array and fully built before removal of the 146GB (the one that hotspared in). Stroller. _______________________________________________ Linux-PowerEdge mailing list [email protected] https://lists.us.dell.com/mailman/listinfo/linux-poweredge Please read the FAQ at http://lists.us.dell.com/faq
