Hi! I wonder do you have a fast link to drop about RAIDedness of EMC storage cache?
Tanel. ----- Original Message ----- To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> Sent: Thursday, August 14, 2003 7:29 PM > > As long as your cache is protected somehow, whether its RAIDed (a la EMC) or > mirrored (a la Hitachi), the vast majority of risk associated with > write-back cache is mitigated. Even with protected cache, I know of a > variety of failure scenarios that will result in loss of in-cache data, but > they definitely fall into the "cascading failure", aka "Act of God", > category of outages. > > Some arrays actually don't even give you the option of write-through cache - > on the symmetrix, for example, it is actually impossible for a write to go > directly to disk. You have no choice but to cache writes. This is called, > in EMC marketing parlance, a "Fast Write". When the cache is under pressure > and the symm decides it needs to make more room in cache for an incoming > write, it holds the write at the host port, flushes an in-cache write to > disk, then places the incoming write in cache and acknowledges it to the > host. This is a "Delayed Fast Write" - I love marketing talk. :) > > Thanks, > Matt > > -- > Matthew Zito > GridApp Systems > Email: [EMAIL PROTECTED] > Cell: 646-220-3551 > Phone: 212-358-8211 x 359 > http://www.gridapp.com > > > -----Original Message----- > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > > Behalf Of Jesse, Rich > > Sent: Thursday, August 14, 2003 11:49 AM > > To: Multiple recipients of list ORACLE-L > > Subject: RE: Storage Cache - WriteThrough or WriteBack > > > > > > Like any good DBA/SA should say "It depends." WriteBack > > gives you better write performance since the IO only needs to > > hit the cache to report back as being completed, whereas > > WriteThru needs to verify the write hit the disk first. > > Either should give the same performance on reads, provided > > the cache isn't the point of contention because of heavy writes. > > > > For our SAN (if we ever get approval for it), we'll probably > > go with WriteBack. The safety factor will be that the cache > > will be mirrored and battery-backed, like you mentioned. > > It's not failsafe (firmware error could conceivably corrupt > > the mirror, too), but I feel that we'd be hitting major > > diminishing returns by going farther than that. You'll have > > to decide what's best for your situation. > > > > BTW, after having someone accidentally kick the power cord > > out of our existing external storage during a server room > > rehaul, I'm going to make sure that we have a copy of the > > control files on a local drive! > > > > HTH! GL! :) > > > > > > Rich > > > > Rich Jesse System/Database Administrator > > [EMAIL PROTECTED] Quad/Tech Inc, Sussex, WI USA > > > > > > > -----Original Message----- > > > From: Tanel Poder [mailto:[EMAIL PROTECTED] > > > Sent: Thursday, August 14, 2003 3:54 AM > > > To: Multiple recipients of list ORACLE-L > > > Subject: Re: Storage Cache - WriteThrough or WriteBack > > > > > > > > > Hi! > > > > > > I usually only tolerate write caching on storage subsystems > > > when we are > > > dealing with expensive boxes like EMCs Clariion or Symmetrix. > > > I too have > > > seen caches fail on entry level boxes like Sun A1000 etc... > > > > > > Tanel. > > > > > > ----- Original Message ----- > > > To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> > > > Sent: Thursday, August 14, 2003 8:39 AM > > > > > > > > > > > > > > I've begun a debate in my organisation about > > > > caches on storage systems. > > > > If an Oracle Database, including Redo Log files, > > > > is on RAID1 or RAID1+0 or RAID5 on the storage/SAN > > > > and the storage/SAN system provides a cache, should > > > > the cache be WriteThrough or WriteBack ? > > > > > > > > I prefer WriteThrough -- particularly when the > > > > Redo Log files are also on such external storage. > > > > > > > > The vendor talks of Mirrored-Caches and Battery-Backed Cache. > > > > > > > > In the past year, we've had one instance of the > > > > Cache itself failing and the Controller stopping all > > > > I/O to the storage and a couple of instances of > > > > Cache batteries being low/dead. {Should I/O be > > > > allowed to proceed if the Cache Batteries are dead > > > > or should the storage automatically switch to WriteThrough ?} > > > > > > > > > > > > Hemant K Chitale > > > > http://hkchital.tripod.com > > -- > > Please see the official ORACLE-L FAQ: http://www.orafaq.net > > -- > > Author: Jesse, Rich > > INET: [EMAIL PROTECTED] > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > > San Diego, California -- Mailing list and web hosting services > > --------------------------------------------------------------------- > > To REMOVE yourself from this mailing list, send an E-Mail message > > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') > > and in the message BODY, include a line containing: UNSUB > > ORACLE-L (or the name of mailing list you want to be removed > > from). You may also send the HELP command for other > > information (like subscribing). > > > > -- > Please see the official ORACLE-L FAQ: http://www.orafaq.net > -- > Author: Matthew Zito > INET: [EMAIL PROTECTED] > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > San Diego, California -- Mailing list and web hosting services > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB ORACLE-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). > -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Tanel Poder INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
