From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Markus_M=FCller?= Subject: Alternative to RAID... No change to Data HDDs, only one simple "modulo"-Disk Date: Fri, 18 Jun 2004 18:12:38 +0200 Sender: linux-raid-owner@vger.kernel.org Message-ID: <40D31476.8020002@pRiV.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi Linux RAID, I don't want Linux Software RAID, because RAID 5 itself and/or the Linu= x=20 Software RAID has unflexibility I don=B4t want to accept. These are esp= ecialy: Implementation independet, logical restrictions: - With only one working disk of a raid 5 I can=B4t do anything, not to=20 mention to mount it alone - I must trust the RAID algorithmus, because it needs and does do=20 writing to handle the data itself - All hdd must be have the same size, ok, you can put langer in it, but= =20 you=B4ll waste space Linux Software RAID restrictions: - Putting new Disk in the RAID is BETA and forces to dataloss The only real advantage is the increased read- and writespeed as well a= s=20 a single partition. And now the clou: I don=B4t care about this advantages! So I prefer the= =20 following solution: You use your hdds as you wouldn=B4t want to use anything like RAID. The= n=20 you insert a new hdd, which have at least the size of the bigest hdd in= =20 computer. Then you make over all hdds for each byte, starting on every=20 disk at byte 0, a modulo 255, and write it to this new disk. Each read=20 access can be done as it would be done before, on every write to one of= =20 these involved hdds you update over all disks the modulo and write it t= o=20 this new disk. If the disks size differs of the different involved hdds= ,=20 you simply have on the higher bytes a modulo of the remaining disks. Fo= r=20 example, you have a 60 GB, a 80 GB and a 120 GB disk. The new disk with= =20 the modulo data is also 120 GBs. Then from 0 byte to 60 GBs you have a=20 modulo over 3 disks, from 60 to 80 you have a modulo over 2 disks and=20 the rest is a 1:1 copy of the 120 GB drive on this new 120 GB disk. -> If a disk dies, you can restore it using the safed modulo data on=20 this new 120 GB disk. The benefit? See the restrictions above. None of this applys on this=20 solution! But you have the same security benefit from RAID 5! The littl= e=20 price for this solution: You loos is speed, and you do not a single=20 partition. I have a data dump, not a high performance raid, so I don=B4= t=20 care about the speed. (Current hdds are fast enought, also for this=20 solution!) And I see multiple partition as a benefit. (personal opinion= !) Special Benefits: - REAL SECURITY: You can resize your hdd selection without having the=20 fear of dataloss! This mechanismus don=B4t change your source hdds! It=20 only does need read access! It CAN=B4T do anything wrong with your data= ! - REAL SECURITY: You can recover with normal rescue programs! - FLEXIBILITY:: You can take any disk out of your system and simply=20 mount it! - FLEXIBILITY: The size of the involved hdds doesn=B4t matter; the disk= =20 with the modulo just must have the same size than the bigest hdd or mor= e=20 of your hdd colletion. And now the matter of price: Does anybody have an idear how to=20 implement this? I am appreciate for any hint or comment. Thanks, Markus Mueller - 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