Linux Tape Device Emulation?

Mon Jan 16 21:46:17 PST 2006

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Jan 16, 2006, at 4:51 PM, Jim Hickstein wrote:

>> Oddly enough, we have the same exact solution from what I've  
>> heard, the Mirapoint! Small world.
>
> :-)  Disclosure: I work for Mirapoint.  But I run my box in  
> production just like anyone else: www.imap-partners.net.

Both facts were known to me, it's a small world we live in :)

>
>> I'm always a bit hesitant to purchase used gear, especially when  
>> it comes to tapes (given the moving parts). Ideally,
>> I'd just hook an lto-3 onto it, and take advantage of the speed  
>> (576gb/hour), which meant if I was at full capacity (100gb)
>> a full backup or restore should be around 20 minutes, which has  
>> it's appeal.. and around a $7k pricetag (for which I
>> could build two very redundant file servers as dedicated backup  
>> servers, and have enough $$ to take my wife out to
>> dinner at French Laundry).
>
> *ahem* Tape speed isn't the primary constraint.  LTO-1s are going  
> for $500 on eBay; I got a couple from a local fellow for less.  Buy  
> two (more if you want to clone tapes and still keep a spare). Spend  
> your money on a _new_ cleaning cart and some _new_ tapes.  They're  
> at the sweet spot on the price curve, too, lately.

The pricing is pretty attractive. I'd like to keep this under $2k for  
the next 3-4 months (realistically, I don't see us growing by more  
than about 500MB per month in the foreseeable future).

> But here's something for nothing: Your Mirapoint box will offline  
> the local tape after every operation -- can't be made not to -- and  
> LTO's (unlike DLT-7000, at least) need human intervention to re- 
> load and read again for a restore.  (A DLT-7000 just turns off the  
> "operate handle" light and carries on.  The LTO you have to stuff  
> back into the slot. Maybe that's not a problem for you.  My 80GB  
> M300 won't fit on a DLT-7000 tape any more.  It's 35/"70", note  
> quotes.)  Via RMT, you can point it at the no-rewind device and  
> otherwise have appropriate control over this.

Annoying, but at least I can get around that by scheduling a tape  
rotation once or twice daily from the noc staff at my colo provider..  
Though, if RMT performs just as well as local tape, then I might as  
well just attach to my backup server, then.

> I measured speed writing to a local DLT-7000 from my M300.  About  
> 4h for 30GB doing 'backup full tape ""' (the default, and fixed,  
> blocksize). Use RMT with the default blocksize ("") via a private  
> 100Base-T network to a FreeBSD 4.6 box with the same drive on a  
> wide SCSI bus, and you're looking at 24h for the same dump.  Crank  
> up the blocksize argument there to 2MB and it's back in the range  
> you expect.  (_That_ was a long weekend in the lab.)
>
> This is the file-by-file dump, and opening files is expensive, so  
> you won't saturate a tape drive, or even 100Base-T necessarily.   
> I'm happy keeping it streaming.  Via NDMP it can do image dumps and  
> get around this, but yes the DMA is in another league.  For now.

Is the speed on an LTO-1 comparable to the dlt-7000, 4 hours for 30GB  
worth of data? This seems really slow.  We have the M450 so perhaps  
the speed has improved somewhat?

>> On the other hand.. lto-1 drives have the capacity I need, and a  
>> good pricepoint .. around $1k it seems.  What do the datadomain
>> boxes look like pricewise?
>
> No idea.  But I used to work for Rex when he was at Mirapoint (he's  
> the King of the SEs at DataDomain now), and I happen to have  
> chatted with him the other day.  Sounds very interesting, but I'm  
> old-school: I like my dumps removable.  Bearings die; heads crash.   
> Yes, tape drives have a lot of moving parts and they're objectively  
> less reliable than disk drives.  But _a given tape_ isn't so bad.   
> And I can afford to be careful: I test my backups routinely.  If it  
> wouldn't wear out my co-lo guys, I'd send two copies offsite every  
> Monday, to two different tectonic plates.

Virtual Tape libraries are appealing. I'm thinking, however, that the  
price point is bound to be just as prohibitive as a higher end backup  
solution that supports NDMP like Veritas, or Legato currently is.  As  
is, this is the only device in our infrastructure with any strict  
need for tapes, so it would be hard to justify. This is one of the  
places where tape is very disappointing as a backup solution to me.  
I'd much rather copy the data to a file server, then just copy the  
deltas (or full images) over the wan to our other datacenters for off- 
sight every night.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (Darwin)

iD8DBQFDzIStwjCqooJyNAMRAqXGAKCIaVLOuBMcfU9oIGhdhSVqd3GCZgCgr7zp
OikuF0tiFB2yXYr2c6tLC5Q=
=6q7b
-----END PGP SIGNATURE-----