Informix Mirroring
Hello, I was reading up on Informix Disk/Chunk Mirroring and was wondering if anyone has any experience using Informix mirroring versus O/S or Hardware mirroring relating to performance? Also, is this a typo in the Informix documentation for mirroring? See the sentences, "On the other hand, when an mirrored chunk goes down, the database server cannot access the data stored on that chunk. If the chunk contains logical-log files, the physical log, or the root dbspace, the database server goes offline immediately." Can that possibly be ? Here is the link to the source Doc: http://publib.boulder.ibm.com/infocenter/idshelp/v115/topic/com.ibm.admin.doc/ids_admin_0799.htm Full Text: Consequences of Not Mirroring If you do not mirror your dbspaces, the frequency with which you have to restore from a storage-space backup after media failure increases. When a mirror chunk suffers media failure, the database server reads exclusively from the chunk that is still online until you bring the down chunk back online. On the other hand, when an mirrored chunk goes down, the database server cannot access the data stored on that chunk. If the chunk contains logical-log files, the physical log, or the root dbspace, the database server goes offline immediately. If the chunk does not contain logical-log files, the physical log, or the root dbspace, the database server can continue to operate, but threads cannot read from or write to the down chunk. If an unmirrored chunk goes down, you must restore it by recovering the dbspace from a backup.
On 3 Feb., 19:04, Dave <in4mix...@gmail.com> wrote: > Hello, > > I was reading up on Informix Disk/Chunk Mirroring and was wondering if > anyone has any experience using Informix mirroring versus O/S or > Hardware mirroring relating to performance? > > Also, is this a typo in the Informix documentation for mirroring? > > See the sentences, "On the other hand, when an mirrored chunk goes > down, the database server cannot access the data stored on that chunk. > If the chunk contains logical-log files, the physical log, or the root > dbspace, the database server goes offline immediately." > > Can that possibly be ? > > Here is the link to the source Doc:http://publib.boulder.ibm.com/infocenter/idshelp/v115/topic/com.ibm.a... > > Full Text: > Consequences of Not Mirroring > If you do not mirror your dbspaces, the frequency with which you have > to restore from a storage-space backup after media failure increases. > > When a mirror chunk suffers media failure, the database server reads > exclusively from the chunk that is still online until you bring the > down chunk back online. On the other hand, when an mirrored chunk goes > down, the database server cannot access the data stored on that chunk. > If the chunk contains logical-log files, the physical log, or the root > dbspace, the database server goes offline immediately. If the chunk > does not contain logical-log files, the physical log, or the root > dbspace, the database server can continue to operate, but threads > cannot read from or write to the down chunk. If an unmirrored chunk > goes down, you must restore it by recovering the dbspace from a > backup. My experience with Informix mirroring is consistently positive. It is a very cost efficient and reliable solution. Regarding the documentation issue: The database server goes only down if the original dbspace/chunk already failed and IDS is already using the mirror chunk. If that one fails as well and is considered a critical dbspace/chunk, IDS will abort. I think that is what the documentation tries to say.
On performance, Informix's testing back in the 90's showed that hardware/firmware mirroring was fastest followed by OS level software mirroring, followed closely by Informix's mirroring. The main reasons to use IDS's mirrors are twofold: - Convenience. You don't have to depend on SAs to manage your mirrors. - Some internal performance gains from parallel reads where IDS has intelligence that the OS or a SAN doesn't. - Normally this is not a big gain. On the other issue, something isn't documented properly. As long as there is an active primary or mirror chunk the engine will stay online. Art Art S. Kagel Advanced DataTools (www.advancedatatools.com) IIUG Board of Directors (art@iiug.org) See you at the 2010 IIUG Informix Conference April 25-28, 2010 Overland Park (Kansas City), KS www.iiug.org/conf Disclaimer: Please keep in mind that my own opinions are my own opinions and do not reflect on my employer, Advanced DataTools, the IIUG, nor any other organization with which I am associated either explicitly, implicitly, or by inference. Neither do those opinions reflect those of other individuals affiliated with any entity with which I am affiliated nor those of the entities themselves. On Wed, Feb 3, 2010 at 1:04 PM, Dave <in4mixdba@gmail.com> wrote: > Hello, > > I was reading up on Informix Disk/Chunk Mirroring and was wondering if > anyone has any experience using Informix mirroring versus O/S or > Hardware mirroring relating to performance? > > Also, is this a typo in the Informix documentation for mirroring? > > See the sentences, "On the other hand, when an mirrored chunk goes > down, the database server cannot access the data stored on that chunk. > If the chunk contains logical-log files, the physical log, or the root > dbspace, the database server goes offline immediately." > > Can that possibly be ? > > Here is the link to the source Doc: > > http://publib.boulder.ibm.com/infocenter/idshelp/v115/topic/com.ibm.admin.doc/ids_admin_0799.htm > > Full Text: > Consequences of Not Mirroring > If you do not mirror your dbspaces, the frequency with which you have > to restore from a storage-space backup after media failure increases. > > When a mirror chunk suffers media failure, the database server reads > exclusively from the chunk that is still online until you bring the > down chunk back online. On the other hand, when an mirrored chunk goes > down, the database server cannot access the data stored on that chunk. > If the chunk contains logical-log files, the physical log, or the root > dbspace, the database server goes offline immediately. If the chunk > does not contain logical-log files, the physical log, or the root > dbspace, the database server can continue to operate, but threads > cannot read from or write to the down chunk. If an unmirrored chunk > goes down, you must restore it by recovering the dbspace from a > backup. > _______________________________________________ > Informix-list mailing list > Informix-list@iiug.org > http://www.iiug.org/mailman/listinfo/informix-list >