The main question you have to ask here is wether you're up to the price (either in money or performance) of a 24/7 full uptime machine. On most cases, assuming only swap resides on a 2nd disk, I would be able to handle a machine crash, and reboot without that swap (as would natrually happen, without any RAID setup), and will suffer happily the 5 minutes downtime assumed by this action. Software RAID (Raid-1) would be very expensive on CPU usage (for each page swap, you need to do a rather intensive usage of your CPU), and other RAID setups gets to be way too expensive for me. Of course, if the server's requirements cannot allow 5 minutes downtime (as a risk, not as a neccessity), then more expensive solutions should be thought of.
Ez. > --=-e2KNw2l4i15uQBuyXGM5 > Content-Type: text/plain > Content-Transfer-Encoding: 7bit > > On Tue, 2005-04-12 at 09:26 +0300, Micha Silver wrote: > >> On the CentOS mailing list, a poster suggested spliting swap space into >> two separate partitions on two drives. Next someone else commented that >> such a scheme would cause a crash if one of the disks with part of the >> swap space died. A third poster answered that it would, and that swap >> space should be mirrored (!). Does this sound correct? I thought that >> splitting swap space across two disks was actually recommended. >> >> Thanks, >> Micha > > > The problem with swap is the "bandwidth" (i.e. the amount of data you > get to/from the swap). Therefore, the wider your "channel" to the swap > space is, the faster it would be. As of today, the bottleneck of swap > space is not the bus between the North/South bridge of the motherboard > to the hard drives, but the speed of the hard drives. Therefore, if your > swap space spans more than one device, you got more bandwidth to it, and > your system runs faster if it uses swap. > > If you take part of the RAM out (and swap space _is_ part of the RAM for > that matter), the machine would die, most probably... The system runs > from that memory :) > > Mirroring the swap space (as in RAID-1), would increase your _reading_ > performance, but not writing (slight performance increase, I guess). > Want really good performance AND machine that doesn't hang if one of the > disks die? Usually more RAM would be less expensive (methinks), but if > you still want the swap, you can use RAID-10 for the swap. That way, > your swap spans two (or more) disks, and is also redundant. But it's > damn expensive :) > > Shimi > > --=-e2KNw2l4i15uQBuyXGM5 > Content-Type: text/html; charset=utf-8 > Content-Transfer-Encoding: 7bit > > <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 TRANSITIONAL//EN"> > <HTML> > <HEAD> > <META HTTP-EQUIV="Content-Type" CONTENT="text/html; CHARSET=UTF-8"> > <META NAME="GENERATOR" CONTENT="GtkHTML/3.2.5"> > </HEAD> > <BODY> > On Tue, 2005-04-12 at 09:26 +0300, Micha Silver wrote: > <BLOCKQUOTE TYPE=CITE> > <PRE> > <FONT COLOR="#000000">On the CentOS mailing list, a poster suggested > spliting swap space into </FONT> > <FONT COLOR="#000000">two separate partitions on two drives. Next someone > else commented that </FONT> > <FONT COLOR="#000000">such a scheme would cause a crash if one of the > disks with part of the </FONT> > <FONT COLOR="#000000">swap space died. A third poster answered that it > would, and that swap </FONT> > <FONT COLOR="#000000">space should be mirrored (!). Does this sound > correct? I thought that </FONT> > <FONT COLOR="#000000">splitting swap space across two disks was actually > recommended.</FONT> > > <FONT COLOR="#000000">Thanks,</FONT> > <FONT COLOR="#000000">Micha</FONT> > </PRE> > </BLOCKQUOTE> > <BR> > The problem with swap is the "bandwidth" (i.e. the amount of > data you get to/from the swap). Therefore, the wider your > "channel" to the swap space is, the faster it would be. As of > today, the bottleneck of swap space is not the bus between the North/South > bridge of the motherboard to the hard drives, but the speed of the hard > drives. Therefore, if your swap space spans more than one device, you got > more bandwidth to it, and your system runs faster if it uses swap.<BR> > <BR> > If you take part of the RAM out (and swap space _is_ part of the RAM for > that matter), the machine would die, most probably... The system runs from > that memory :)<BR> > <BR> > Mirroring the swap space (as in RAID-1), would increase your _reading_ > performance, but not writing (slight performance increase, I guess). Want > really good performance AND machine that doesn't hang if one of the disks > die? Usually more RAM would be less expensive (methinks), but if you still > want the swap, you can use RAID-10 for the swap. That way, your swap spans > two (or more) disks, and is also redundant. But it's damn expensive :)<BR> > <BR> > Shimi > </BODY> > </HTML> > > --=-e2KNw2l4i15uQBuyXGM5-- > > > ================================================================= > To unsubscribe, send mail to [EMAIL PROTECTED] with > the word "unsubscribe" in the message body, e.g., run the command > echo unsubscribe | mail [EMAIL PROTECTED] > > ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
