Les Mikesell lesmikesell@gmail.com wrote:
Even if they permit drives to move between different models it still means you have to have a spare compatible one handy if your primary box dies.
Not always. There are ways to map various hardware RAID-0 and 10 block-striped volumes in Linux MD or LVM (via DeviceMapper), including 3Ware. RAID-1 is no issue at all, it's just a mirror.
RAID-5 is the only one that differs greatly.
You can mount one partition out of an md RAID1 set directly as the underlying partition, bypassing any concern about compatibility of md versions if you need to recover data. LVM is a different story.
MD hasn't always been that good, but only in more recent kernels. I've been using 3Ware since late kernel 2.0.
Nothing against the 3Ware cards - I agree they are very good, although you did forget to mention the various bugs they have had and fixed over those 6+ years.
Bugs have been limited to RAID-5 limitations.
First off, they should have never implemented RAID-5 on the Escalade 6000. It's ASIC was never designed for it.
Secondly, I have repeatedly stated that the ASIC+SRAM approach in even the 7000/8000 series is for non-blocking I/O, and not good for a buffering/XOR operation like RAID-5 writes. It's fine if you largely just read from the RAID-5 volume, but tanks on RAID-5 writes (although it's can be far better than software RAID when rebuilding).
Lastly, I have _never_ been a proponent of the Escalade 9500S, and recomended people stick with the 8506 and use RAID-10. Their recent introduction of the Escalade 9550SX series which adds an embedded PowerPC tells me that the ASIC design, even with DRAM added (in the 9500S), would never be a good performer for RAID-5 writes. But I'm hopeful we'll see great things out of the 9550SX series.
Until someone shows me an application that RAID-5 is faster than RAID-10, I will stick with RAID-10. With ATA drives as cheap as they are, getting a few extra GBs is not worth the write performance gains of RAID-10. And RAID-10 load balances reads better than RAID-5.