Date: Wed, 01 Oct 2008 10:03:02 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> Cc: Jeremy Chadwick <koitsu@freebsd.org>, Danny Do <ai_quoc@hotmail.com>, freebsd-questions@freebsd.org Subject: Re: Optimal File System config for 2.5TB RAID5 Message-ID: <48E33CC6.7050504@infracaninophile.co.uk> In-Reply-To: <20081001083637.C7317@wojtek.tensor.gdynia.pl> References: <1222681181.48e0a25d094c3@www.inbox.lv> <BAY139-DAV13C8982A51CD9B05C74D5090430@phx.gbl> <48E21C66.8080407@FreeBSD.org> <BAY139-DAV5423DFBF403B32AA0C22690430@phx.gbl> <20080930161407.E16761@wojtek.tensor.gdynia.pl> <BAY139-DAV45B9F2CCF6913F5533E3090430@phx.gbl> <20080930205435.B20033@wojtek.tensor.gdynia.pl> <00ee01c92346$69508fa0$3bf1aee0$@com> <20080930224447.GA58065@icarus.home.lan> <20081001083637.C7317@wojtek.tensor.gdynia.pl>
next in thread | previous in thread | raw e-mail | index | archive | help
-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 Wojciech Puchar wrote: |> |> What you're asking for is "too much" -- and this conversation is |> starting to delve into freebsd-hardware, not freebsd-questions. | | the simple answer is that software RAID on todays computers vastly | outperforms ANY hardware raid solution, maybe except the ones for 10000$ | or more. You're basically correct, but I think you're overestimating the price of a good RAID controller. The big win with hardware RAID controllers comes when they are fitted with a BBU. Typically this turns a £400 item into a £600 item, so most sales weasels will artfully forget to include it[+]. When you've got a BBU, then it lets you do the good stuff like disable write cache on the drives but *enable* it on the controller -- the presence of the battery means that data cached in RAM is safe and in the event of an unscheduled reboot, it can be flushed to disk as the system comes up again -- so the RAID can justifiably report to the OS that the IO transaction is complete without having to wait for the bits to actually hit the disk platter[*]. I've occasionally wondered why there isn't a simple device commonly available which consists of a few hundred MB of battery backed (or otherwise persistent in the face of power loss) RAM that can plug into a PCI slot and fulfil that function generically for any disks in a machine. Solid state hard drives are getting there, but they're still too expensive and not really fast enough yet. Cheers, Matthew [+] And I don't know how the manufacturers justify that price tag, as the battery tech used is based on the same off-the-shelf components that go into any mobile phone [*] Unlike the normal hw.ata.wc enable, which reports this unjustifiably... - -- Dr Matthew J Seaman MA, D.Phil. Flat 3 ~ 7 Priory Courtyard PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate ~ Kent, CT11 9PW, UK -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEAREDAAYFAkjjPMYACgkQ3jDkPpsZ+VYBGwCgmIndkiis5+OfA8ahXCbTasxO pbkAn2y69JagZweBpD62TnctqtQdt+mF =yHzW -----END PGP SIGNATURE-----
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?48E33CC6.7050504>