On 30/5/03 6:17 pm, "scott.marlowe" <[EMAIL PROTECTED]> wrote:
> On Fri, 30 May 2003, Adam Witney wrote: > >> Hi scott, >> >> Thanks for the info >> >>> You might wanna do something like go to all 146 gig drives, put a mirror >>> set on the first 20 or so gigs for the OS, and then use the remainder >>> (5x120gig or so ) to make your RAID5. The more drives in a RAID5 the >>> better, generally, up to about 8 or 12 as the optimal for most setups. >> >> I am not quite sure I understand what you mean here... Do you mean take 20Gb >> from each of the 5 drives to setup a 20Gb RAID 1 device? Or just from the >> first 2 drives? > > You could do it either way, since the linux kernel supports more than 2 > drives in a mirror. But, this costs on writes, so don't do it for things > like /var or the pg_xlog directory. > > There are a few ways you could arrange 5 146 gig drives. > > One might be to make the first 20 gig on each drive part of a mirror set > where the first two drives are the live mirror, and the next three are hot > spares. Then you could setup your RAID5 to have 4 live drives and 1 hot > spare. > > Hot spares are nice to have because they provide for the shortest period > of time during which your machine is running with a degraded RAID array. > > note that in linux you can set the kernel parameter > dev.raid.speed_limit_max and dev.raid.speed_limit_min to control the > rebuild bandwidth used so that when a disk dies you can set a compromise > between fast rebuilds, and lowering the demands on the I/O subsystem > during a rebuild. The max limit default is 100k / second, which is quite > slow. On a machine with Ultra320 gear, you could set that to 10 ot 20 > megs a second and still not saturate your SCSI buss. > > Now that I think of it, you could probably set it up so that you have a > mirror set for the OS, one for pg_xlog, and then use the rest of the > drives as RAID5. Then grab space on the fifth drive to make a hot spare > for both the pg_xlog and the OS drive. > > Drive 0 > [OS RAID1 20 Gig D0][big data drive RAID5 106 Gig D0] > Drive 1 > [OS RAID1 20 Gig D1][big data drive RAID5 106 Gig D1] > Drive 2 > [pg_xlog RAID1 20 gig D0][big data drive RAID5 106 Gig D2] > Drive 3 > [pg_xlog RAID1 20 gig D1][big data drive RAID5 106 Gig D3] > Drive 4 > [OS hot spare 20 gig][g_clog hot spare 20 gig][big data drive RAID5 106 > Gig hot spare] > > That would give you ~ 300 gigs storage. > > Of course, there will likely be slightly less performance than you might > get from dedicated RAID arrays for each RAID1/RAID5 set, but my guess is > that by having 4 (or 5 if you don't want a hot spare) drives in the RAID5 > it'll still be faster than a dedicated 3 drive RAID array. > Hi Scott, Just following up a post from a few months back... I have now purchased the hardware, do you have a recommended/preferred Linux distro that is easy to configure for software RAID? Thanks again Adam -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
