The Drobo’s battery only helps Drobo “finish its last writes” - it doesn’t prevent filesystem corruption due to the computer being “cut off” mid-access.
Rechargeable batteries also have variable lifespan, so I’d still recommend a UPS for the Drobo and a computer directly attached to it.
This way, in the event of a power outage, the UPS will notify the computer that the power has gone out, and the computer can go through its normal shutdown/hibernate procedure and stop writing data to the Drobo. Then when the Drobo itself loses power, no data is actively writing. The possibility of filesystem corruption is reduced tremendously compared to the attached computer just losing power without a proper shutdown.
[quote]The Drobo’s battery only helps Drobo “finish its last writes”[/quote].
Ok, here is where I am confused regarding how the internal Drobo Battery is used/comes into play. Specifically:
… So, when AC Power is lost during writing to the Drobo, is the Drobo Internal Battery used to save the “last writes” in a memory chip and then applied when the AC Power is returned to the Drobo "
… Or, does the Drobo Internal Battery have enough power to run all the drives in the Drobo to apply the “Last Writes”, when the AC Power is cut off during writing to the Drobo ?
drobo hold it in memory and does clever maths to make it redundant <---- this step
drobo writes data to multiple drives
the one i have labelled - is what drobo’s battery savers … the data it has been passed by the pc but has not yet committed to disk - its buffer/cache if you will[hr]
you can still royally mess up your file system if it looses power tho - by no means would i count on its internal cache to be a good indication of file integrity.
Ah, so it can then apply anything left in drobo memory chip, when the AC power returns. provided the AC power returns before the drobo battery exhausts it self in the 24hr - 48 hr range that the drobo battery holds its charge. … Is this right ?
i think in theory that is correct, but snice what is in its memory may be only half of a write frmo the comptuer - it may be useless.
i THINK the battery is more designed so that if you arent writing or doing anything on your drobo… it may be doing its own internal housekeeping when you loose power… and the battery will prevent its own internal filesystem from becoming corrupted due to power loss.
i.e. anything drobo is doing by itself wont cause damage with a power loss. writes you do from your pc will probably cause minor corruption if you loose power.
… I understand now the importance of also having a UPS and I think I may need to get one, eventhough …
… I have my Drobo connected to a Laptop PC (which I am using as a Desktop PC replacement, when the Laptop is on the desk and not in transit), I guess that I should still connect my Laptop PC to a UPS (as well as, connecting the Drobo to the UPS), in order to have an Automated controlled shutdown of the Laptop PC to protect the file system integrity;
… in case I am not around to manually shutdown the Laptop PC, before the Laptop PC’s Battery is exhuasted
– OR –
… in case the Laptop PC has just started the process of Re-charging its Battery (after returning it to my desk, re-connecting it to the Drobo and powering on the Drobo) and has not yet gained enough charge to power it for a manual shutdown and then unluckily a power outage occurs at this point in time ?
What do you think ???
… I know many people say a UPS is not needed for a Laptop PC, but I am thinking now to protect against file system integrity issues when using a laptop to write to a connected Drobo that one should still have a UPS for the Laptop PC with a a connected Drobo for the reasons that I stated above ?
I think that eventhough I use a Laptop PC (with the Drobo connected to the Laptop PC) that I still need a UPS, based on my above thoughts ???
… Need experts with more experience than myself to comment on my above thoughts/conclusions ?
Based on what you described (repeated below), and to ensure that I got the complete picture correct) let me know if you concur with my below understanding and conclusion, based on what you outlined above:
The issue is that the Drobo will “cut off” when the power is lost.
OS is writing to Drobo.
Power goes out. Drobo is disconnected (because it loses power). Laptop is still running on battery power.
Laptop can’t “talk” to Drobo anymore.
The problem is #2 - the OS may not have completed its write process when the Drobo disappears - it’s like pulling the USB/Firewire connection without properly ejecting first.[/quote]
Likewise then, the problem with connecting the UPS only to the Drobo and relying on the Laptop PC’s Battery is …
… If the UPS cuts power to the Drobo, beforethe Laptop PC’s Battery exhaustsitself (a laptop pc’s battery will usually outlast the UPS battery time by a large margin, when fully charged), then its the same problem that you desscribed above in "For example, … Items 1 - 3.
So, then the answer is,that both the Drobo and the Laptop PC need to both be connected to a UPS, (so that the pending writes are completed) and to ensure there’s no danger of corruption. … Do you concur with this conclusion ?
what bhiga was trying to say is that the laptop doesnt need UPS POWER - it would still need the data connection to the ups so that the laptop can shut itself down when the power supplied to the drobo (from the UPS) is running low.
that way the laptop can monitor the ups and its own internal battery and as soon as either runs low, it will shutdown, after that it doesnt matter when the drobo looses power
Now, I understand what bhinga was tring to say, Yes, I see now that the important aspect here is that “the laptop pc would still need the data connection to the ups so that the laptop can shut itself down when the power supplied to the drobo (from the UPS) is running low”.
… However, I just have a few remaining questions, before ending this thread:
1. But, would there be any significant disadvantage to also plugging the laptop pc into the UPS’s battery outlet ?
2. I would think that an advantage to also plugging the laptop pc into the UPS’s battery outlet would be the added benefit of getting “Line conditioning/AVR”, when the AC is present abd the AC is experiencing under voltage/over voltage conditions, as to provide additional protection to the laptop pc’s power brick ?
3. What do you find to be the best Nunber of Minutes to set in the UPS software to perform the graceful hibernation shutdown ?
… For example, smothing like "when only 5 minutes of UPS Battery time remains, perform the unattended hibernation shutdown ?
it would run down the UPS - its more sensible to let the ups power the drobo, and let the laptop use its own internal power.
from my limited knowledge of physics (three degrees ) i think the transformer and the fact the voltage is stepped down so low protects you from anything which would really affect your laptop.
5 minutes is fairly typical, especially if its only a hibernate and not a shut-down (i.e. it doenst need to wait for programs to close)
HOWEVER from memory i dont think computers tend to like drives being “missing” when they wake up from a hibernate/standby - which would happen if the power was out and you needed to power your laptop back on using its internal battery but your UPS was still out of juice - you would be turning on your laptop and leaving drobo off, so i would recommend getting ti to shutdown not hibernate then you can be sure its completely closed any processes which were using drobo (plus i imagine this (power failure) is not a scenario you are expecting very often, so a full reboot woudlnt be the end of the world)