linux-kernel - RE: Announcement: STEC EnhanceIO SSD caching software for Linux kernel

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Date:	Thu, 31 Jan 2013 03:56:06 +0800
From:	Amit Kale <akale@...c-inc.com>
To:	Pavel Machek <pavel@....cz>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: RE: Announcement: STEC EnhanceIO SSD caching software for Linux
 kernel

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@....cz]
> Sent: Wednesday, January 30, 2013 4:37 AM
> To: Amit Kale
> Cc: LKML
> Subject: Re: Announcement: STEC EnhanceIO SSD caching software for
> Linux kernel
> 
> Hi!
> 
> > 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.
> >
> > The source volume to SSD mapping is a set-associative mapping based
> on the source volume sector number with a default set size (aka
> associativity) of 512 blocks and a default block size of 4 KB.  Partial
> cache blocks are not used.
> > The default value of 4 KB is chosen because it is the common I/O
> block
> > size of most storage systems.  With these default values, each cache
> > set is 2 MB (512 *
> > 4 KB).  Therefore, a 400 GB SSD will have a little less than 200,000
> cache sets because a little space is used for storing the meta data on
> the SSD.
> >
> > EnhanceIO supports three caching modes: read-only, write-through, and
> write-back and three cache replacement policies: random, FIFO, and LRU.
> >
> > Read-only caching mode causes EnhanceIO to direct write IO requests
> > only to HDD. Read IO requests are issued to HDD and the data read
> from
> > HDD is stored on SSD. Subsequent Read requests for the same blocks
> are
> > carried out from SSD, thus reducing their latency by a substantial
> > amount.
> 
> What are the requirements for the SSD? I have 500GB 2.5" HDD in the
> notebook... and it starts to be slightly slow for git. Would cheap 8GB
> USB stick be useful thing to cache at? (USB sticks have reasonably fast
> "seek", but reads are in 20MB/sec range and writes are very
> slow.)

Hi Pavel,

Our testing primarily covered 100GB+ SSDs due to our focus on enterprise market. 8GB will work, but 500:8 is about 60times. Our recommendation is to keep SSD:HDD ratio between 1:5 and 1:10. I'll be most interested in knowing your findings.

Thanks.
-Amit

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