SATA hot swap

[Bill McGonigle]

On 06/17/2009 10:33 PM, Ben Scott wrote:
>   Really.  That's very interesting.  Can you elucidate?  Years ago,
> 3Ware was practically synonymous with high-quality ATA controllers,
> and were an early contributor of GPL drivers for such.  They've
> certainly had enough time to go downhill since then, but I'd like to
> know details.

Yeah, I had been buying them on momentum myself.  It seems to be very
hit-or-miss in the past few years, though, depending on the particular
board.  Some of my favorites, from various controllers:

* 3-minute 'sync' times.  Disks check out fine on other controllers,
linux disk cache is small.
* JBOD modes that don't actually export any disks.
* On ones that do, importing a disk as JBOD wipes out the first 512
bytes of the disk silently (recoverable with a backup of the partition
table, but, guys... play nice with others)
* spotty detection of new disks inserted (tw_cli rescan finds 'em but
the kernel doesn't seem them all the time when freshly inserted)
* sluggish performance in all-but 'performance' mode, which doesn't seem
to best any $20 AHCI controllers.

I often find folks commiserating on 3ware message boards about such
problems when I hit them, but they don't seem to be addressed.  I just
looked and there is one recent firmware update I haven't tired on a
troublesome board, which 'improves ext3 write performance'.  But that
machine has been in service for almost two years.

Part of the problem may be that I'm often asking 3ware boards to do
things that aren't their typical RAID use cases, since I usually wind up
doing software RAID for performance and portability and also because
many of my clients don't care to inventory on-site cold spares or
redundant infrastructure.  Maybe those areas aren't as heavily QA'ed.
With the advent of mobos which commonly have 8+ SATA ports and add-in
cards with several more for small coin, I'm not finding I actually need
them much anymore.

For certain sets of problems, though: non-journaled filesystems on
machines without UPS's (and the battery-backup add-on for the
controllers), highly-parallel disk rates that would saturate the PCIe
bus, etc. there are still some good reasons to buy them.

-Bill

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