Re: [PATCH 1/1] ipr: Fix for adapter shutdown issue

[James Bottomley <James.Bottomley@SteelEye.com>]

On Wed, 2005-06-15 at 11:11 -0500, Brian King wrote:
> System crash and controlled power off are two different things. Yes, if the
> adapter is not told about the shutdown so it can flush its cache, the
> data will be maintained, but it can only be maintained for as long as
> the battery lasts. Currently, with 2.6.12-rc, if you do a normal power off
> and leave the system powered off for a long enough period of time (usually
> a week or so, depending on the battery on the card), you will suffer data
> loss. This is not acceptable. With 2.6.11, the adapter is told to flush
> the write cache on a controlled power off, so the system can remain powered
> off indefinitely with no data loss.
> 
> Regarding supporting the sync cache command to a disk array, I did consider
> requesting support be added to the adapter microcode, but decided against it
> since it would make a RAID array perform horribly and it did not seem to be
> the appropriate model to follow for NV write cache. Some of the ipr adapters
> have over 500 MB of write cache, which can take an awful long time to flush,
> much longer than you would want for a journal barrier. So, all the barrier/
> SYNC_CACHE code works great for a volatile write cache on a disk, but
> doesn't necessarily seem like the best model for large non-volatile write
> caches for RAID adapters.

Well, I still think you're operating unsafely ... some people let these
batteries run out, you know ...

To fix this, add a

blk_queue_ordered(sdev->request_queue, QUEUE_ORDERED_NONE);

to the slave configure routine for each of the devices that doesn't
synchronize the cache.  That should correct the SCSI layer assumptions.

James