Date: Tue, 27 Jul 2010 16:35:12 +1000 From: David Rawling <djr@pdconsec.net> To: freebsd-questions@freebsd.org Subject: Re: 1 file system, 2 drives? Message-ID: <4C4E7E20.3020005@pdconsec.net> In-Reply-To: <4C4DF5F1.4080109@identry.com> References: <4C4DDA28.4070205@identry.com> <980022A0-7623-40A5-BCDE-4909A721933D@mac.com> <4C4DF067.7000801@identry.com> <4C4DF5F1.4080109@identry.com>
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On 27/07/2010 6:54 AM, John Almberg wrote: > John Almberg wrote: >>> If you have hardware controller with RAID capabilities, using native >>> RAID is better, otherwise look towards gvinum or maybe ccd; see also: >> I've just been reading up on RAID in my Absolute FreeBSD book, and it >> occurs to me that my client has a SCSI RAID drive chassis that he is >> using stupidly... >> >> It's a 14 bay drive, and he's currently got seven 32G drives stuck in >> it, configured with RAID-0. This is the original 200G drive I was >> talking about. It's a few years old. >> >> Over the next few years, this guy is going to need lots of storage >> for his videos. >> >> After a bit of reading, I'm wondering if the best idea might be to >> toss out those 32G drives and replace them with 3 big (say, 300G) >> drives configured with RAID-5. It sounds to me like a RAID-5 array >> can be expanded by adding new drives. >> >> QUESTION: is expansion normally a matter of just plugging in a new >> drive? Is the new drive automatically grafted onto the old drives? Or >> do you have to go through a process like, backing up the data, >> plugging in the new drive, reformatting the expanded array of drives, >> and restoring the data. >> >> I don't know the brand/model of the RAID drive chassis, but the >> client thinks it can be switched to use RAID 5. I'm waiting for the >> technical details, but assuming it can handle RAID-5 for now. > Answering my own question... > > So its a HP 6402 / 128 RAID controller. From a quick skim of the > manual, it looks like the controller has to go through an 'expansion' > process when adding a new drive. This sounds time consuming, but more > or less automatic -- i.e., handled by the controller. > > Sounds like this might be the best way to go. It's been a while since I dealt with HP SCSI RAID, but ISTR that you'd need to install and configure the 3 disks as a RAID 5 set, copy the data from the 7x36GB array to the new array, (using a temporary mount point, generally, and dump | restore) switch the mount points across so that the /videos tree is the new copy, then remove the RAID0 set from the controller. You may or may not find that the RAID controller changes LUN IDs after a cold start too, so LUN 1 (new RAID 5) suddenly becomes LUN 0 on the cold start after the old RAID set is decommissioned and pulled. This is often accompanied by a heart attack on the part of the person restarting the server. After that, though, expansion is a cinch - but it will be quite slow since it needs to read and write the entire content of all disks. I'd therefore go as many spindles as you can - 3 disks, 5 disks and 9 disks are what I recall as being optimal groups for RAID 5. Also consider that you can supplement the RAIDs with the BSD tools previously mentioned. Today is 3 x 300GB. Tomorrow add another 3 x 300 (assuming IOPS is OK) and concatenate them to be a 1.8TB "disk" - 2D+P + 2D+P. Dave. -- David Rawling PD Consulting And Security Mob: +61 412 135 513 Email: djr@pdconsec.net
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