At 02:57 PM 4/9/99 -0400, Bruce B. Platt wrote:
Over the weekend, I received the following from Alan Davis
<Davis_at_Tessco.Com>, which I quote in it's entirety, since it completely and
succinctly describes why secondary swap configured via LSM MUST be in the
rootdg disk group:
"In the Release Notes. This is from the v4.0e release :
------- begin excerpt
4.6.6.2 Restrictions with LSM root and swap Volumes
Root, primary swap, and secondary swap volumes configured under LSM have the
following restrictions:
Root and primary swap must be on the same physical disk and you must
configure them using the encapsulation tools.
If a secondary swap volume is configured under LSM, you must configure the
root and primary swap.
You must configure the root, primary swap, and any secondary swap volumes
into the disk group named rootdg.
------- end excerpt
If you want to know /why/ :-)
1. The swapon command will be very confused, thinking that there is an error
on the primary swap device. Swap is checked before LSM comes up all the way,
only the rootdg volume is available when swapon needs it's stuff.
2. Swap devices do double duty as dump devices, ie when a system crashes,
the kernel image is written first to primary swap and if necessary to
additional swap devices if it doesn't all fit into primary. The dump code
doesn't allow for secondary swap outside of rootdg. This is also why all
swap devices must be LUN0.
Alan Davis
Tru64 Unix Consultant"
Thank you Alan!
->Thanks to:
->
-><alan_at_nabeth.cxo.dec.com>
->John Speno <speno_at_isc.upenn.edu>
->Davis <Davis_at_Tessco.Com>
->George
->Guethlein <gguethlein_at_giantofmaryland.com>
->
->I had asked where is the "best" place to put a secondary swap mirror set,
->full question below.
->
->Paraphrasing the answers the consensus was that there is no performance
->penalty or benefit resulting from placement of rootdg.
->
->Alan suggested that since it was unlikely the volume would ever be "shared"
->in a cluster sense, rootdg was the place for it.
->
->John thought he remembered reading that secondary swap had to be in rootdg.
->
->George felt the logical place for secondary swap was in rootdg since swap
->is a "system" entity, though he adheres to the practical logic of placing
->volumes in disk groups named by function.
->
->I quote Davis since he was emphatic: "It is clearly documented that any
->swap space defined on LSM volumes /must/
->be in the rootdg disk group."
->
->Davis, I don't doubt you, but would you happen to have a reference, since I
->can't find one.
->
->I appreciate all your answers, and your speed. If I can, I will try it
->both ways tomorrow and see what happens, I am in an empirical mood. But,
->you can bet I'll do it first with swapvol2 in rootdg, do a volsave, put the
->db files in a safe place, then take it apart and put swapvol2 in another
->disk group. I'm not about to mess up a production system with 320 GB of
->data across 80 spindles in six disk groups!
->
->Thanks, folks,
->
->Regards
->
->
->
->
->------------------------------------------------------------
->Never having added any additional swap space to an LSM configuration,
->before, I am faced with the question of where
->(in what disk group) to place a mirrored swap volume which I will call
->swapvol2 which will be a secondary swap file.
->
->I fail to find any hints in all the documentation available as to which
->disk group, rootdg, or a separate one is the best group in
->which to place this volume for performance.
->
->It seems to me that since I am using a system where /, primary swap, /usr,
->and /var are mirrored and are in rootdg, it would make sense to add my new
->swap volume to a new disk group named "moreswap" or something equally
->descriptive.
->
->However, I have no information other than that provided by intuition that
->it makes any difference in performance or reliability as to which disk
->group I place swapvol2. It certainly makes the LSM layout more
->understandable to have swapvol2 in a separate disk group, but that's all i
->know for sure.
->
->Anyone have any suggestions?
->
->Thanks in advance and of course I'll summarize.
->
->Regards,
->
->Bruce
->
->+--------------------------------------+
->Bruce B. Platt, Ph.D.
->Comport Consulting Corporation
->78 Orchard Street, Ramsey, NJ 07446
->Phone: 201-236-0505 Fax: 201-236-1335
->bbp_at_comport.com, bruce_at_ bruce.platt_at_
->OR, bruce_at_bbplatt.com
->
+---------------------------------------------------------+
Bruce B. Platt, Ph.D. Vice-President
Comport Consulting Corporation
78 Orchard Street
Ramsey, NJ 07446
Phone: 201-236-0505 Fax: 201-236-1335
bbp_at_comport.com, bruce.platt_at_comport.com, bruce_at_comport.com
OR, bruce_at_bbplatt.com
Received on Mon Apr 12 1999 - 14:18:32 NZST