Date: Tue, 01 Feb 2000 07:23:37 -0700 From: "Justin T. Gibbs" <gibbs@FreeBSD.org> To: Greg Lehey <grog@lemis.com> Cc: "Justin T. Gibbs" <gibbs@plutotech.com>, Gary Palmer <gjp@in-addr.com>, scsi@FreeBSD.org, up@3.am, Wilko Bulte <wilko@yedi.iaf.nl> Subject: Re: hardware vs software stripping Message-ID: <200002011423.HAA15471@caspian.plutotech.com> In-Reply-To: Your message of "Tue, 01 Feb 2000 19:04:41 %2B1030." <20000201190440.Q76348@freebie.lemis.com>
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>> RAID-3 is the same as RAID4 without the optimization for partial >> stripe writes. In otherwords, in RAID-3, you must read or write a >> full stripe where RAID-4 adds the ability to perform RMW operations >> on the parity block of the stripe for sub-stripe updates. > >I'm not sure I follow you here. Are you saying that the data layout >is the same and the difference is in the implementation of the >software? That doesn't seem to justify a separate level. In RAID3, there is no restriction on the per-drive blocking factor. In RAID4, it is supposed to be a multiple of your transaction size so you can perform partial read (assuming you don't need parity verification) and RMW operations to update the parity for updating contiguous transactions that are not as large as the stripe. >> Pluto uses a RAID-3 system in its video server products and it is >> certainly not striped on a byte level. > >So how exactly is it striped? Our stripe size is 1-2MB with the per-drive stripe component size varying depend on the number of drives in the system. >> (Just as an aside, given the minimum 512 byte sector size of most >> magnetic media, striping an a per byte basis would be really >> wasteful). > >Agreed, unless you use a PLA to split the data. > >Obviously, the manufacturer of your RAID-3 box uses the term >differently from the way it's defined above. Pluto makes its own RAID hardware. 8-) -- Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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