Tony, I'm pretty sure I understand RPO and RTO correctly. I'm used to
teach it.
However please, take care - we talk about backup copy only, not about
the system.
We don't know whole system setup and components. We know that tape
waiting for PTAM (truck delivery to secondary DC) cause some additional
period between backup is finished and backup is available in secondary
data center. Of course any backup on tape is being done periodically, so
one could loose some data between backups. That's true despite of backup
replication/delivery method - however delivery process or asynchronous
replication process adds extra time to this window.
Last but not least: sometimes it is possible to recover from last
existing backup only, previous copy is marked as unusable or it's hard
to use it.
In such scenario your systeme (DASD replicated) could be aware of last
backup, but your last backup is not delivered and will never be
delivered because of fire on server room.
Regards
--
Radoslaw Skorupka
Lodz, Poland
W dniu 31.01.2020 o 17:44, Tony Thigpen pisze:
Radoslaw,
I think you don't understand RPO correctly.
read:
https://www.enterprisestorageforum.com/storage-management/rpo-and-rto-understanding-the-differences.html
Tony Thigpen
R.S. wrote on 1/31/20 11:24 AM:
W dniu 31.01.2020 o 07:07, Timothy Sipples pisze:
Radoslaw Skorupka wrote:
To complement and clarify: when using physical tapes (*
see below) your RPO and RTO may be 36 hours or zero.
No, your RPO certainly won't be zero. A backup is a (hopefully useful)
representation of data as it existed historically, at some
particular past
moment(s) in time. It takes some amount of time to run a backup --
let's
call that "minutes or longer" for working purposes. Backups run at
periodic intervals -- let's call that "hourly or less often" for
working
purposes. Your backups, without something else, facilitate a best
case RPO
that's as long/big as the maximum (worst case) time elapsed since the
start of your last good backup. That practically always(*) means a
RPO of
"a couple hours or more."
A long/big RPO usually holds RTO back too, but there are a few rare
exceptions. On the other hand, it's quite possible to have a
long/big RTO
with a RPO of zero.
(*) Why not "always"? Exotic, contrived exceptions might be
possible, such
as custom software that synchronizes writes directly to local and
remote
tape.
No, my RPO *is* zero. We do not talk about backup itself, which is
...the same for VTS, MAGSTAR, USB stick, etc. Despite of backup media
the backup is representation of historical data.
What I'm talking about is time delta between primary and secondary
(local, remote) backup copies.
And again: some (typical?) modes of VTS replication are not
synchronous, so there is time delta between local copy is closed (and
marked as done) and remote copy is also finished. For duplex write in
HSM both tapes are being written simultaneously, so end of backup job
means you have both copies ready.
Note: Earlier you mentioned that PTAM makes RPO longer. Yes, it
*adds* the time to "historical representation". VTS non-synchronous
mode adds the time also (much less). but HSM duplex write add zero.
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
.
======================================================================
Jeśli nie jesteś adresatem tej wiadomości:
- powiadom nas o tym w mailu zwrotnym (dziękujemy!),
- usuń trwale tę wiadomość (i wszystkie kopie, które wydrukowałeś lub zapisałeś
na dysku).
Wiadomość ta może zawierać chronione prawem informacje, które może wykorzystać
tylko adresat.Przypominamy, że każdy, kto rozpowszechnia (kopiuje, rozprowadza)
tę wiadomość lub podejmuje podobne działania, narusza prawo i może podlegać
karze.
mBank S.A. z siedzibą w Warszawie, ul. Senatorska 18, 00-950
Warszawa,www.mBank.pl, e-mail: kont...@mbank.pl. Sąd Rejonowy dla m. st.
Warszawy XII Wydział Gospodarczy Krajowego Rejestru Sądowego, KRS 0000025237,
NIP: 526-021-50-88. Kapitał zakładowy (opłacony w całości) według stanu na
01.01.2019 r. wynosi 169.347.928 złotych.
If you are not the addressee of this message:
- let us know by replying to this e-mail (thank you!),
- delete this message permanently (including all the copies which you have
printed out or saved).
This message may contain legally protected information, which may be used
exclusively by the addressee.Please be reminded that anyone who disseminates
(copies, distributes) this message or takes any similar action, violates the
law and may be penalised.
mBank S.A. with its registered office in Warsaw, ul. Senatorska 18, 00-950
Warszawa,www.mBank.pl, e-mail: kont...@mbank.pl. District Court for the Capital
City of Warsaw, 12th Commercial Division of the National Court Register, KRS
0000025237, NIP: 526-021-50-88. Fully paid-up share capital amounting to PLN
169.347.928 as at 1 January 2019.
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
