From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: RAID0 - cache Date: Thu, 20 Jan 2011 07:20:16 +1100 Message-ID: <20110120072016.1b2162c8@notabene.brown> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Roberto Spadim Cc: Linux-RAID List-Id: linux-raid.ids On Wed, 19 Jan 2011 18:13:23 -0200 Roberto Spadim wrote: > Hi guys, from a long email i will start this one: (the last one wasn=B4= t send) >=20 > think about this: >=20 > /dev/sda (sata disk 1000gb size, latency of 1ms to move head, 100mb/s > to write/read) > /dev/sdb (ssd 1gb size, latency of <100us to find what flash and > position, 500mb/s to write/read) > ram memory (8gb size, with 1gb not used) > /dev/mdxxx (the new device i=B4m calling it as raid0-cache) >=20 > how raid0-cache work? >=20 >=20 > how to create raid? > tell what the sequencial read cache estrategy: > memory(tell fixed memory size) - /dev/sdb - /dev/sda - another device > (maybe just 2 is suficiente /dev/sdb and /dev/sda)... >=20 >=20 > how to read? > first, read from the first read device (memory) > if information not there -> read from second read device (/dev/sdb), > update information at first read device, return the read value > if information not there -> read from third read device (/dev/sda), > update information at second and first read device, return the read > value >=20 > how to write? > flush space from first read device to second read device > write to first read device, return OK >=20 > background thread: > sync from first write device (memory) to second write device (/dev/sd= b) > flush from second write device (/dev/sdb) to third write device (/dev= /sda) >=20 > startup: > using cache: > flush everythink from first write device (memory) to second write > device (/dev/sdb) > flush everythink from second write device (/dev/sdb) to second write > device (/dev/sda) > since memory is volatille, at startup it can=B4be flushed... > without cache: > make first write device unusable (memory) > make second write device unusable > here we can have write problems, since a wrong power off, can lost > information from cache (first and second write device) >=20 >=20 >=20 > anyidea who can make it? "Hey, I've got this clever idea, I wish someone would implement it" alm= ost always results in ... nothing. People with the ability to implement are much more interested in implem= enting their own ideas. But see also "bcache". NeilBrown > thanks > -- > Roberto Spadim > Spadim Technology / SPAEmpresarial > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html