Re: Fwd: [ADSM-L] Lun versus logical volume for DB volumes
DB2 doesn't know whether it's an actual LUN or not. It only sees the filesystem. Whether you use dedicated LUNs is a performance question. On XIV type disk where I/O is striped every which way and everything is spinning all the time, it's a whole different question than if you put 8 filesystems on one physical LUN (which would be madness). Point is, if you aren't using dedicated LUNs (and with XIV I don't think the concept applies), it's up to you to put the filesystems on something that can deliver the performance so you don't have long response times on the disk. I can tell you that in my experience on much cheaper, lowest-end hardware (to go into detail would be too embarrassing at this point - oh to have an XIV *and* an SVC!! I have hardware envy), I picked up support of a TSM Windows server with the DB on 1 directory. As the load grew we moved the DB to 4 directories on the same Megaraid array, then to 4 directories on a DDP array, then 8 directories on the DDP array, and got more throughput through the data base at each step. So it does make a difference to DB2, up to the point where the hardware can't deliver the IOps. What I would like to know, is how to ask DB2 when it's queue is backed up so we would know when there would be a performance improvement if it had more logical LUNs to write to. There's gotta be a way to do that, but I have no clue how. Wanda -Original Message- From: ADSM: Dist Stor Manager [mailto:ADSM-L@VM.MARIST.EDU] On Behalf Of Steven Harris Sent: Wednesday, July 16, 2014 8:43 AM To: ADSM-L@VM.MARIST.EDU Subject: [ADSM-L] Fwd: [ADSM-L] Lun versus logical volume for DB volumes Thanks Ron for the reply Its actually moot as the back end is XIV behind SVCs. But the SAN guys like to allocate standard size luns and my DB luns are all a bit small for their liking, so if I could get the same multithread effect by allocating one big lun, with multiple AIX VGs on it, that would be happiness. Regards Steve. On 16 July 2014 13:05, Ron Delaware wrote: > Steven, > > The logical volumes are not dedicated disks in most cases, which means > that other applications may be using the same disks at the same time. > With our new "TSM Server Blueprint" standards, TSM database's over 1TB > require > 16 luns. > > You can go to this link to find out more > > > https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki > /Tivoli%20Storage%20Manager/page/NEW%20-%20Tivoli%20Storage%20Manager% > 20Blueprint%20-%20%20Improve%20the%20time-to-value%20of%20your%20deplo > yments > > > > Best Regards, > > _ > * Ronald C. Delaware* > IBM Level 2 - IT Plus Certified Specialist – Expert IBM Corporation | > Tivoli Software IBM Certified Solutions Advisor - Tivoli Storage IBM > Certified Deployment Professional Butterfly Solutions Professional > 916-458-5726 (Office > 925-457-9221 (cell phone) > > email: *ron.delaw...@us.ibm.com* > > From: Steven Harris > To:ADSM-L@vm.marist.edu > Date:07/15/2014 06:55 PM > Subject:[ADSM-L] Lun versus logical volume for DB volumes > Sent by:"ADSM: Dist Stor Manager" > -- > > > > Hi, > > I've specced a design for a new TSM server and as recommended have > specified multiple luns for the database. The folklore is that DB2 > will start one thread per lun so for a big database you use 8 luns and > hence get > 8 threads. > > My AIX guy is asking whether I really need 8 luns or will 8 AIX > logical volumes have the same effect. > > Does anyone know or can tell me where to look? > > Thanks > > Steve. > > Steven Harris > TSM Admin > Canberra Australia > > >
Re: Lun versus logical volume for DB volumes
> allocating one big lun, with multiple AIX VGs on it In AIX, a lun is part of a vg. A single lun can only be part of a single vg. Our experience with big databases is with Oracle on AIX. AIX has 2 levels of queues: - on the hba (lsattr -El fcsX | grep num_cmd_elems) - on the lun (lsattr -El hdiskY | grep queue_depth) Your backend with SVC/XIV means that you shouldn't hit disk hot spots on the storage array. This is really good. One problem you can hit is to max out the queue of the host hba, SVC hba or XIV hba. The AIX fcs depth can be seen in the above lsattr cmd. If the AIX fcs queue is full, AIX waits. If the queue at the SVC/XIV is full, that system sends a cmd back to the host saying to stop sending. This causes a slowdown. Since multiple servers probably share the SVC ports, there can be a problem if the aggregate server I/O's fill the SVC port queue. AIX iostat has a stat for tracking if this occurs (sqfull???). This is one reason for having multiple hba's on a server into the SAN, feeding multiple ports on the SVC, into multiple ports on the XIV is really helpful. Be sure the luns are set to algorithm round-robin to make use of multiple paths to the lun. I assume the SVC has the same idea for the backend I/O's to the XIV via multiple paths. There is also a queue for each lun. If your AIX application (DB2, Oracle, whatever) pounds a single lun (hdisk), you can max out this queue. So while you may have lots of backend IOPS in the SVC/XIV, you may not be able to get I/O's through to them. This is why a single big lun in AIX isn't really good. You can raise the queue size of the lun. You can also spread your database/application across multiple luns. For our big systems we allocate lots of luns and spread the AIX VG physical partitions across all the luns (maximum parm of the vg). When we add a lun to a server like this, we then do a reorgvg to re-spread the physical partitions so that all luns are performing I/O. (If you have a hot spot that fits within a single physical partition, there's not much you can do about it!) Think of a lun as having two characteristics: capacity and IOPS. Capacity is easy to get and use up, IOPS can be much harder to get and use. With your SVC in the middle you have 3 levels of virtualization to figure out and handle: AIX LVM (vg's and lv's), the SVC (IOGROUPS, pools, mdisks???, not sure what all), and finally the XIV (different heads and extents spread across all disks).This multiple levels of stripping is called a PLAID. It's really good for random workloads, but can be bad for sequential processing! Interesting . . . doesn't DB2 do some kind of stripping across the separate filesystems you can give the db, and, has limits on concurrent I/O's per filesystem That would make a 4th levels of stripping and tuning!! A, things are so simple! (not) Rick -Original Message- From: ADSM: Dist Stor Manager [mailto:ADSM-L@VM.MARIST.EDU] On Behalf Of Steven Harris Sent: Wednesday, July 16, 2014 8:43 AM To: ADSM-L@VM.MARIST.EDU Subject: Fwd: [ADSM-L] Lun versus logical volume for DB volumes Thanks Ron for the reply Its actually moot as the back end is XIV behind SVCs. But the SAN guys like to allocate standard size luns and my DB luns are all a bit small for their liking, so if I could get the same multithread effect by allocating one big lun, with multiple AIX VGs on it, that would be happiness. Regards Steve. On 16 July 2014 13:05, Ron Delaware wrote: > Steven, > > The logical volumes are not dedicated disks in most cases, which means > that other applications may be using the same disks at the same time. > With our new "TSM Server Blueprint" standards, TSM database's over 1TB > require > 16 luns. > > You can go to this link to find out more > > > https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki > /Tivoli%20Storage%20Manager/page/NEW%20-%20Tivoli%20Storage%20Manager% > 20Blueprint%20-%20%20Improve%20the%20time-to-value%20of%20your%20deplo > yments > > > > Best Regards, > > _ > * Ronald C. Delaware* > IBM Level 2 - IT Plus Certified Specialist – Expert IBM Corporation | > Tivoli Software IBM Certified Solutions Advisor - Tivoli Storage IBM > Certified Deployment Professional Butterfly Solutions Professional > 916-458-5726 (Office > 925-457-9221 (cell phone) > > email: *ron.delaw...@us.ibm.com* > > From:Steven Harris > To:ADSM-L@vm.marist.edu > Date:07/15/2014 06:55 PM > Subject:[ADSM-L] Lun versus logical volume for DB volumes > Sent by:"ADSM: Dist Stor Manager" > -- > > > > Hi, > > I've specced a de
Fwd: [ADSM-L] Lun versus logical volume for DB volumes
Thanks Ron for the reply Its actually moot as the back end is XIV behind SVCs. But the SAN guys like to allocate standard size luns and my DB luns are all a bit small for their liking, so if I could get the same multithread effect by allocating one big lun, with multiple AIX VGs on it, that would be happiness. Regards Steve. On 16 July 2014 13:05, Ron Delaware wrote: > Steven, > > The logical volumes are not dedicated disks in most cases, which means > that other applications may be using the same disks at the same time. With > our new "TSM Server Blueprint" standards, TSM database's over 1TB require > 16 luns. > > You can go to this link to find out more > > > https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/Tivoli%20Storage%20Manager/page/NEW%20-%20Tivoli%20Storage%20Manager%20Blueprint%20-%20%20Improve%20the%20time-to-value%20of%20your%20deployments > > > > Best Regards, > > _ > * Ronald C. Delaware* > IBM Level 2 - IT Plus Certified Specialist – Expert > IBM Corporation | Tivoli Software > IBM Certified Solutions Advisor - Tivoli Storage > IBM Certified Deployment Professional > Butterfly Solutions Professional > 916-458-5726 (Office > 925-457-9221 (cell phone) > > email: *ron.delaw...@us.ibm.com* > > From:Steven Harris > To: ADSM-L@vm.marist.edu > Date:07/15/2014 06:55 PM > Subject:[ADSM-L] Lun versus logical volume for DB volumes > Sent by:"ADSM: Dist Stor Manager" > -- > > > > Hi, > > I've specced a design for a new TSM server and as recommended have > specified multiple luns for the database. The folklore is that DB2 will > start one thread per lun so for a big database you use 8 luns and hence get > 8 threads. > > My AIX guy is asking whether I really need 8 luns or will 8 AIX logical > volumes have the same effect. > > Does anyone know or can tell me where to look? > > Thanks > > Steve. > > Steven Harris > TSM Admin > Canberra Australia > > >
Re: Lun versus logical volume for DB volumes
Steven, The logical volumes are not dedicated disks in most cases, which means that other applications may be using the same disks at the same time. With our new "TSM Server Blueprint" standards, TSM database's over 1TB require 16 luns. You can go to this link to find out more https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/Tivoli%20Storage%20Manager/page/NEW%20-%20Tivoli%20Storage%20Manager%20Blueprint%20-%20%20Improve%20the%20time-to-value%20of%20your%20deployments Best Regards, _ Ronald C. Delaware IBM Level 2 - IT Plus Certified Specialist – Expert IBM Corporation | Tivoli Software IBM Certified Solutions Advisor - Tivoli Storage IBM Certified Deployment Professional Butterfly Solutions Professional 916-458-5726 (Office 925-457-9221 (cell phone) email: ron.delaw...@us.ibm.com Storage Services Offerings From: Steven Harris To: ADSM-L@vm.marist.edu Date: 07/15/2014 06:55 PM Subject: [ADSM-L] Lun versus logical volume for DB volumes Sent by:"ADSM: Dist Stor Manager" Hi, I've specced a design for a new TSM server and as recommended have specified multiple luns for the database. The folklore is that DB2 will start one thread per lun so for a big database you use 8 luns and hence get 8 threads. My AIX guy is asking whether I really need 8 luns or will 8 AIX logical volumes have the same effect. Does anyone know or can tell me where to look? Thanks Steve. Steven Harris TSM Admin Canberra Australia
Lun versus logical volume for DB volumes
Hi, I've specced a design for a new TSM server and as recommended have specified multiple luns for the database. The folklore is that DB2 will start one thread per lun so for a big database you use 8 luns and hence get 8 threads. My AIX guy is asking whether I really need 8 luns or will 8 AIX logical volumes have the same effect. Does anyone know or can tell me where to look? Thanks Steve. Steven Harris TSM Admin Canberra Australia
