Hi, why not to the list? On EMC (if used as synonym for EMC Symmetrix...) cache is normally that big, that all your I/O goes to a 'virtual solid state disk'. I know some EMC devices and i am still impressed about their product. But to completely separate your mirrored log disks you would need to use two separate 'directors (I-O channel boards)' inside the EMC. In such a case even a failure of a EMC director board would be tolerated. You 'log devspaces' inside the EMC would also be mirrored and striped inside the EMC. That is the maximum precaution you can do on the hardware side. But you have to decide how much money you spend for that.
The DUAL mode doubles the number of devspaces you need. If you wanted 2 log devspaces before, you would add 2 mirrored log devspaces. If you use one of your former two devices for the mirror, you end up with half the capacity of the log volume... CU jrg > -----Original Message----- > From: Nguyen, Bao L [mailto:[EMAIL PROTECTED]] > Sent: Dienstag, 14. Januar 2003 22:49 > To: Mensing, Joerg > Subject: RE: LiveCache 7.4 - Should I use Dual Log Mode or Not? > > > Hello Joerg, > > Thank you very much for your recommendations! I believe that > we could utilize the dual log mode since we can put the log > and the mirrored log onto separated EMC disks (their disk > activities will not collide). > > Also, we currently have 2 log devspaces configured for SINGLE > log mode. In order to change to DUAL log mode, do I need to > create 2 respective mirrored log devspaces or I only need to > create 1 mirrored log devspace ? > > Thanks & Regards. > > Bao Nguyen > > -----Original Message----- > From: Mensing, Joerg [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, January 14, 2003 4:43 AM > To: Nguyen, Bao L; [EMAIL PROTECTED] > Subject: RE: LiveCache 7.4 - Should I use Dual Log Mode or Not? > > > > -----Original Message----- > > From: Nguyen, Bao L [mailto:[EMAIL PROTECTED]] > > Sent: Freitag, 10. Januar 2003 22:45 > > To: [EMAIL PROTECTED] > > Subject: LiveCache 7.4 - Should I use Dual Log Mode or Not? > > > > > > Hi All, > > > > According to the "Checklist for recovery of SAP APO liveCache > > 7.4" by Werner Thesing, it is recommended to mirror the > > LiveCache log in production. However, I concern about the > > impact on Livecache performance if we use the dual log mode > > for our Livecache 7.4. How much the dual log mode can impact > > to Livecache performance in contrast to the single log mode? > > > > Thanks. > > > > Bao Nguyen > > > > Bao L. Nguyen > > SAP APS SE Team > > Ph: 916-356-0705 > > Pgr: 916-857-2755 > > > Hi, > this is not a liveCache specific issue, but for all SAPDB instances. > > If you use a separate controller and disks for the mirrored > log devices, you will not loose performance notable, since > writing activity on both disk is done asynchrously in > separated threads for each device. Only if the mirrored log > devices writing collides with other disk activity, you will > loose performance. > > During reading from log (restart) you will even gain > performance, since the reading is done like in a RAID 1 > hardware (reading from both disks can be done in > parallel...). Another good reason to keep the log devices > separated from other disk activity, is that log information > is written in streaming mode on the disk, which is only fast, > if no other seek activity happens on that disk in parallel... > > So independent from your disk choice, for best software > performance and security use separated log devices - which > are really for log only - on separated controllers in a dual > log configuration. > CU > jrg > _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
