RAID
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Contents
R.A.I.D.
Quick Overview
Okay, with properly run hardware RAID, RAID 1 is the slowest (Data's written to both drives at the speed of the slowest drive), RAID 5 is next fastest (As the data spans the drives, so it's 1/3 faster than a single drive or RAID 1), and RAID 0 is the very fastest (Data's written to both drives simultaneously). If you have the drives to spare (4 drives), and you don't mind "Losing" half the capacity for the backup, then RAID 0+1 is the best combination, giving high speed AND data redundancy (50% capacity, 200% preformance). If you don't have the drives (3 drives), or you wish to get more capacity from the drives you have, then RAID 5 is best, as it gives you 66% of the capacity of the drives and 133% of the performance. If you have only 2 drives, you can opt to use them as RAID 1 (Which will give you 50% capacity and 100% performance) or RAID 0 (Which gives you 100% capacity (And 0% redundancy), and 200% performance). This is all assuming you're using hardware RAID, which is not reliant on CPU overheads or anything like that. Software RAID changes this, as it uses the CPU and the regular IDE controller, but can't (generally) write to multiple drives simultaneously. -- Robert "Anaerin" Johnston
RAID For Recordings Drive
A few Options exist for using RAID for the Recordings drive, epending on the goal you have for your recordings drive, speed or redundency, or both. RAID 1 Will allow you to gain the most speed from your drives, RAID 01(or RAID 0+1) will give you speed and 1:1 redundency, and RAID 5 sits inbetween, giving you a slight speed increase over RAID 0 but with parity to recreate the data on a failed drive.
With HD becoming the prevalent standard...
RAID For Archives Drive
Having an independent drive array for archival of shows one wishes to keep allows the user to setup a RAID for speed for the recordings drive and a RAID for backup for the archival drive. This way, once a show has been recorded, commercial flagged and possibly even transcoded to another format or for permanent commercial removal, it can be moved to the archive. In such a case, RAID 5 and RAID 01 make the most sense. If you plan on a large amount of access to the archive, a RAID 01 will make the most sense as it will most easily keep up with the transfer rate requirement while still allowing for redundency, but at the cost of the price for obtaining the number of drives requried. RAID 5 will have a slight speed advantage over just having numerous drives (JBOD, Just a Bunch Of Disks), but will also have the advantage of getting the most archival bang-for-your-buck while still maintaining parity for the case of a lost drive.
Links
Great page with information on the different hardware and software raid chipsets, their current linux support
Wikipedia Entry for RAID
mdadm MAN page (via man-wiki)
Software-RAID HOWTO
--Steveadeff 19:00, 8 January 2006 (UTC)
