[dm-devel] [RFC] [DONOTAPPLY] [PATCH] enhanceio: STEC EnhanceIO SSD caching software for Linux kernel

[Kent Overstreet]

On Thu, Feb 07, 2013 at 06:57:40AM +0800, Amit Kale wrote:
> > -----Original Message-----
> > From: Michel Lespinasse [mailto:walken at google.com]
> > Sent: Friday, February 01, 2013 4:58 PM
> > To: Darrick J. Wong
> > Cc: Amit Kale; linux-bcache; device-mapper development; Kent
> > Overstreet; Mike Snitzer; LKML; Jason Warr; thornber at redhat.com
> > Subject: Re: [RFC] [DONOTAPPLY] [PATCH] enhanceio: STEC EnhanceIO SSD
> > caching software for Linux kernel
> > 
> > On Fri, Feb 1, 2013 at 4:44 PM, Darrick J. Wong
> > <darrick.wong at oracle.com> wrote:
> > > This is a patch to migrate STEC's enhanceio driver out of their
> > github
> > > repository and into the staging tree.  From their README:
> > >
> > > "EnhanceIO driver is based on EnhanceIO SSD caching software product
> > > developed by STEC Inc. EnhanceIO was derived from Facebook's open
> > > source Flashcache project. EnhanceIO uses SSDs as cache devices for
> > > traditional rotating hard disk drives (referred to as source volumes
> > throughout this document).
> > > EnhanceIO can work with any block device, be it an entire physical
> > > disk, an individual disk partition,  a RAIDed DAS device, a SAN
> > > volume, a device mapper volume or a software RAID (md) device."
> > 
> > What's your take on the benefits of this vs bcache ?
> 
> EnhanceIO was designed for and has been validated in enterprise environments. The important benefits are - 
> 1. There is no downtime for cache creation, deletion, editing properties, writeback/readonly/writethrough mode change.

True of bcache.

> 2. Wb mode comes with an option to control whether dirty data should be clean-up across reboots, which prevents SSD/HDD going out of sync.

No idea why you'd want this. You have to be able to handle a rebooting
with a dirty cache, if you hope to handle unclean shutdown - bcache does
this. And if you're running in writeback mode there's probably going to
be many gigabytes of dirty data in your cache, at least sometimes, and
you aren't going to want to wait for that to flush before you reboot.

If you want to flush dirty data with bcache, you can switch back to
writethrough mode whenever you want.

> 3. Our in-house testing was done for large setups with 500GB+SSDs and proportionately large HDDs, on 24CPU machines with plenty of RAM. It's survived heavy IO loads without any locking or corruption problems.

True of bcache.

> 4. Error handling is exactly what enterprises look for - writethrough/readonly modes work seamlessly regardless of SSD failures. In all the three caching modes, the guarantees of completion in presence of IO errors or shutdowns, in terms of granularity and persistence of data written, is identical to underlying HDDs.

True of bcache.

> 5. It works for all known block devices - Software RAIDs, full block devices with or without partitions, individual partitions, various intelligent block devices.

True of bcache.

> -Amit
> 
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Which of the above information was proprietary, and should I not be
resending this to lkml or - who?

...