Thanks for the clear and complete answer. I shall try it also over here :-) (53GB DB)
Regards, Maurice ----- Original Message ----- From: "Daniel Sparrman" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, August 01, 2005 11:20 AM Subject: Re: [ADSM-L] @Sparrman: mirrorwritedb parallel - tried it? No, thats not correct. The pageshadowfile is used to store the database entry until it has been commited to all database volumes so in that way you are protected against partial writes. The write to the pageshadow file is not sequntial, the write is written to the pageshadowfile at the same time the write it sent to your datbase copies and stored there until a commit has been recieved from every database copy. Btw, you cannot even use pageshadowing unless you have enabled parallel write against the database volumes. >From the TSM manual (ref: http://publib.boulder.ibm.com/infocenter/tivihelp/v1r1/topic/com.ibm.itsmaixn.doc/anrarf53499.htm): "Specifies whether database page shadowing is enabled. If database page shadowing is enabled, Tivoli Storage Manager mirrors every write to a database page. You can enable shadowing only if database volume mirrors are written to in parallel (that is, the MIRRORWRITE DB option is set to PARALLEL). The default is YES. For more information on specifying mirroring and database page shadowing server options, see " Protecting and Recovering Your Server" in the Administrator's Guide." >From the Administrator's Guide; "Protecting and Recovering Your Server" (ref: http://publib.boulder.ibm.com/infocenter/tivihelp/v1r1/topic/com.ibm.itsmaixn.doc/anragd53701.htm): "MIRRORWRITE specifies how mirrored volumes are written to. You may issue MIRRORWRITE LOG or DB, and then specify that write operations for the database and the recovery log be specified as SEQUENTIAL or PARALLEL: A PARALLEL specification offers better performance but at the potential cost of recoverability. Pages are written to all copies at about the same time. If a system outage results in a partial page write and the outage affects both mirrored copies, then both copies could be corrupted. A SEQUENTIAL specification offers improved recoverability but at the cost of performance. Pages are written to one copy at a time. If a system outage results in a partial page write, only one copy is affected. However, because a successful I/O must be completed after the write to the first copy but before the write to the second copy, performance can be affected." "DBPAGESHADOW=YES mirrors the latest batch of pages written to a database. In this way if an outage occurs that affects both mirrored volumes, the server can recover pages that have been partially written. If no name is specified in the DBPAGESHADOWFILE option, a dbpgshdw.bdt file will be created and used. If the DBPAGESHADOWFILE option specifies a file name, that file name will be used. " Best Regards Daniel Sparrman ----------------------------------- Daniel Sparrman Utvecklingschef Exist i Stockholm AB Propellervägen 6B 183 62 TÄBY Växel: 08 - 754 98 00 Mobil: 070 - 399 27 51 Maurice van 't Loo <[EMAIL PROTECTED]> Sent by: "ADSM: Dist Stor Manager" <[email protected]> 2005-08-01 11:01 Please respond to "ADSM: Dist Stor Manager" <[email protected]> To [email protected] cc Subject @Sparrman: mirrorwritedb parallel - tried it? ----- Original Message ----- From: "Daniel Sparrman" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, August 01, 2005 9:31 AM Subject: Re: [ADSM-L] mirrorwritedb parallel - tried it? *cut* The security risk is mainly in a scenario were TSM writes to both of the db volumes and crashes at the same time. This could result in a partial write = database restore. To avoid this security issue when using parallel writes, enable pageshadowing with "dbpageshadow yes" and "dbpageshadowfile FILENAME". The pageshadowfile should preferable be placed on separate disks from the TSM database volumes. *cut* If you use parallel writes and dbpageshadow, aren't you do sequential writing again? As far as i know, dbpageshadow is used with hardware-mirror in stead of TSM-mirror, so there is still a sequential write possible. So if you use parallel writes for a better performance and use dbpageshadow, you still use sequential writes between the real db and the shadow and lose the performance bennefit. Regards, Maurice
