Date: Sat, 17 Feb 2007 22:14:01 -0800 From: Garrett Cooper <youshi10@u.washington.edu> To: freebsd-questions@freebsd.org Subject: Re: gvinum with RAID capable SATA card Message-ID: <45D7EEA9.3090205@u.washington.edu> In-Reply-To: <45D77DFA.9090504@infracaninophile.co.uk> References: <45D77216.40308@u.washington.edu> <45D77DFA.9090504@infracaninophile.co.uk>
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Matthew Seaman wrote: > Garrett Cooper wrote: >> Hello, >> Motherboards usually don't support more than 2 SATA ports, and since >> SATA is 1:1, I have to invest in a SATA RAID card to get RAID-5 support. >> After reading the handbook a bit I came across chapter 19, which >> goes into some detail about why and how to the configure one's disks in >> a software RAID with gvinum. However, I'm not sure what mode (if one >> exists) that I could put a RAID card in to make the OS see single disks. >> So I guess my point is, can I turn off RAID functionality on the >> card and make the disks into single, separated disks available via the >> disk controller, or is that impossible with a RAID card? >> I think the problem lies with my (limited) knowledge of RAID. > > Most RAID controllers certainly will support acting in JBOD mode. > Check the docco before buying. Ok, sounds good. > However, if you've got a hardware RAID card, then you'll almost > certainly be better off using it for doing RAID5 than doing it in > software with gvinum. The RAID card will have hardware to do the > parity calculations needed for RAID5 and offloading that from the > CPU is a big win. Well, it may be in a sense, but I'm afraid of controller reliability and the whole proprietary nature of RAID cards.. I don't want a controller maker to be bought up by another group a few years from now and I won't be able to use my drives because they don't exist :(.. > The balance of advantage between hardware and software RAID is not so > clear cut for RAID1 or RAID10 (mirror or mirror+stripe). Software RAID > is a lot cheaper, can be monitored by native system tools and is pretty > much as performant as hardware RAID unless you have a battery backup > unit on the RAID card [in which case you can set the card to tell the OS > the data is secure as soon as it is in battery backed RAM on the card > (which takes nanoseconds) rather than actually written to disk (which > takes milliseconds), hence decreasing IO latency enormously]. > > When buying a RAID card, an important consideration is that there > are FreeBSD compatible management tools available -- otherwise, for > example, you'll not get alerted to disk problems other than by the > onboard alarm buzzer on the card. > > Cheers, > > Matthew Hmmm.. for my intentions though it would be purely personal data storage, so while speed would be wonderful it's not as necessary. I'm mostly aiming for storage size and reliability. Thanks for the comments though; they were helpful :). -Garrett
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