ADSM-L

Re: restore times

2015-10-04 17:46:04
Subject: Re: restore times
From: Dusedau, Stefan
To: ADSM-L AT VM.MARIST DOT EDU
Kelly,

We do not have collocation turned on since we could not afford the number
of
tapes it would require. I just ran a simple SQL (select node_name, count(*)
from volumeusage group by node_name). This produces a list of how many
volumes contain data for each node on the server. The top hitter is a node
that has been backing up for 26 months and uses 1036 volumes. Of course
this
includes drm copies, archives and inactive copies so the actual number for
a
restore will be less. I have spoken with IBM about this on several
occasions
and they have recommended exporting and importing the nodes. This would
probably take a week to do for a node using 500 tapes. By the way we have
our copy group setup as VERE=7 VERD=1 RETE=45 RETO=60.

Also, I have found that the average tape mount on a 3494 is between 30 and
60 seconds. This is for 5 3494s connected to AIX and AS/400 environments so
I believe that it is the 3494s not the operating system.

I am interested in to hear what others have done to help in this area.

Thank You,

Stefan Dusedau
infoWorks
A Viacom technology service
(212)258-6739
stefan.dusedau AT viacom DOT com <mailto:stefan.dusedau AT viacom DOT com>


                -----Original Message-----
                From:   Kelly J. Lipp [mailto:lipp AT storsol DOT com]
                Sent:   Tuesday, March 16, 1999 6:09 PM
                To:     'Dusedau, Stefan'
                Subject:        RE: restore times

                I don't think the reclamation process would spread data on
that many tapes.
                 I wonder what actual experience will show with a system
that has been
                running for a year or more.


                Kelly J. Lipp
                Storage Solutions Specialists, Inc.
                www.storsol.com
                lipp AT storsol DOT com
                (719)531-5926

                -----Original Message-----
                From:   Dusedau, Stefan
                Sent:   Tuesday, March 16, 1999 1:08 PM
                To:     'lipp AT storsol DOT com'
                Subject:        RE: restore times

                Kelly,

                I agree with most of what you said regarding tape mounts.
The one
                difference
                is that 30 day retention does not mean 30 tapes. If you
nave
a node that
                has
                been backing up for a year and file "A" has not changed or
been deleted in
                that time, it may be on any of the hundreds of tapes that
have been used
                during reclamation. Now multiply this by the number of
files
that do not
                change often and you have spread your data across more
tapes
then the last
                30 days have used.

                Thank You,

                Stefan Dusedau
                infoWorks
                A Viacom technology service
                (212)258-6739
                stefan.dusedau AT viacom DOT com
<mailto:stefan.dusedau AT viacom DOT com>


                                -----Original Message-----
                                From:   Kelly J. Lipp
[mailto:lipp AT STORSOL DOT COM]
                                Sent:   Tuesday, March 16, 1999 11:30 AM
                                To:     ADSM-L AT VM.MARIST DOT EDU
                                Subject:        Re: restore times

                                If one does a realistic examination of
restore times, tape
                mounts, unless
                                you have very slow tapes, usually won't
come
into play.

                                Let's start the discussion with service
level agreements.
                For instance,
                                all of us should have in place agreements
with our customers
                that sound
                                something like this:

                                1. For single file restores, we offer a
restore time of one
                hour or less.
                                2. For a directory tree restore up to 200
MB, we offer a
                restore time of
                                one hour or less.
                                3. For a full disk restore up to 4 GB, we
offer a restore
                time of four
                                hours or less.
                                4. For a full system restore up to 100 GB,
we offer a
                restore time of 24
                                hours.

                                Wiggle these to meet your needs.

                                Think about what many of us can offer now.
Are the numbers
                above
                                reasonable from a business standpoint?
 Most
of us state
                we'll do it as
                                fast as possible when we should be putting
in place SLAs
                that more
                                accurately reflect reality.

                                Restore statistics:

                                99% of restores are for single files, or
small numbers of
                files from
                                yesterday.  Not a problem with ADSM.
                                1% of the restores are bigger than this:
complete
                directories, all the data
                                for an application, a complete disk, a
complete system.
                This flat does not
                                happen very often, but one should be
concerned (but not
                overly so) about
                                it.

                                Let's look at the larger restores.  Pick a
hard one like the
                full disk
                                restore.  Assume a 30 day data retention
(verdeleted,
                verexists, retextra,
                                retonly all set to 30).  Worst case, 30
tape
mounts will be
                required during
                                a full restore of the disk.  Most of the
data will be on the
                first tape
                                with small amounts scattered on the rest of
the 30.  In
                fact, looking at
                                typical usage, the same files tend to
change
so the same
                files will show up
                                on many of the tapes.  So during a restore,
these files will
                only be
                                restored once, and perhaps from the most
recent tape.  Tape
                mounts just
                                went way down.

                                But let's keep it at 30 mounts.  Say each
mount takes two
                minutes and the
                                time to reach data is another minute for a
total of three
                minutes per tape.
                                 Then we can do some real work and move
data.  For this
                case, we'll expend
                                90 minutes of our four hour window.  Are we
in trouble?  I
                don't think so.
                                 We should meet our SLA for this restore.
Will we actually
                need to mount
                                30 tapes?  Probably not, since we've got
reclamation going
                on as well.

                                If tape mounts really become a problem, and
I'm maintaining
                this is the
                                least of your worries about large restores,
one can always
                use collocation
                                to reduce them.

                                Think about your data.  It's usage and its
change patterns.
                Think about
                                your other protection mechanisms: RAID,
shadowing, etc.
                Think about your
                                restore requirements and SLAs.  For those
of
you still
                believing GFS
                                (Grandfather, father, son) backups are
still
better, think
                about this: you
                                have to mount all of the incrementals
between a full even
                though most of
                                same files change everyday.  Using this
method, more files
                are actually
                                restored and then deleted than ADSM would
actually restore!

                                BTW, one should test the restore times
before publishing
                SLAs.  However, if
                                one applies reason and logic, this just
isn't all that hard.

                                Thanks,

                                Kelly J. Lipp
                                Storage Solutions Specialists, Inc.
                                www.storsol.com
                                lipp AT storsol DOT com
                                (719)531-5926

                                -----Original Message-----
                                From:   McAllister Craig-WCM033
                                Sent:   Tuesday, March 16, 1999 9:00 AM
                                To:     ADSM-L AT VM.MARIST DOT EDU
                                Subject:        Re: restore times

                                That certainly appealed to me at one point,
however, this
                will "push" one
                                version of your files out of the queue you
have made from
                your management
                                class. (Selective backup will keep two
copies of exactly the
                same file, and
                                may push one older, different version out
into expiration)
                                For this reason, perhaps if you want this
type of
                functionality, you should
                                be looking at file archival, rather than
backup.

                                It certainly works for me.

                                        -Craig.

                                -----Original Message-----
                                From: Fluker, Tom R
[mailto:Tom.Fluker AT VIASYSTEMS DOT COM]
                                Sent: 16 March 1999 15:34
                                To: ADSM-L AT VM.MARIST DOT EDU
                                Subject: restore times


                                It appears to me that one of the problems
with restores
                taking so long is
                                that the incremental nature of ADSM will,
over time, spread
                the required
                                files over many volumes in a tape storage
pool.  Requiring
                mounts, and
                                searches, of multiple tapes requires a lot
of time.

                                Has anybody tried, say once a month,
performing selective
                backups for
                                entire
                                file systems in an effort to aggregate all
the files
                required for a restore
                                in reasonable proximity to each other?
Incremental backups
                would then get
                                scattered but it may limit the number of
tapes that would be
                required.
                                Would this help the restore time problem?

                                I'm considering such an idea and was
wondering if anybody
                has had any
                                similar experiences that may help.

                                Tom Fluker
                                Tom.Fluker AT viasystems DOT com
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