LTO-7 Question about capacity

[Frank Cherry]

Hi There,

I use Ultrium 7 tapes with 6 / 15 TB storage capacity. So I do expect a minimum of 6 TB in worst case (without compression).

Now a tape was marked as full. There are two jobs with 1.15 and 1.4 TB = 2.55 TB.
A running job wants to despool 1,198,389,602,186 bytes.
During despooling, end of medium was reached:
End of medium on Volume "CRFull-0012" Bytes=3,314,676,943,872

and Bareos asks for a new volume in this pool to append.

When I now calclulate the present 2.55 TB + 1,2 TB in queue = 3,75 TB, less than 6 TB for LTO-7

Has anyone an explantation for this please? The tape was new.
At the moment, a new tape was add to the pool and the backup continuous.

Thaks for helping, Frank

[Wolfgang Denk]

Dear Frank,

In message <9d042448-250b-467a...@googlegroups.com> you wrote:
>
> I use Ultrium 7 tapes with 6 / 15 TB storage capacity. So I do expect a
> minimum of 6 TB in worst case (without compression).

...

> When I now calclulate the present 2.55 TB + 1,2 TB in queue = 3,75 TB, less
> than 6 TB for LTO-7

The spec for LTO 7 gives a sustained data rate of 300 MB/s. Check
if your storage daemon can feed the drive with such a rate;
otherwise the drive will run in start-stop mode which is slow, causes
increased wear on the drive and the tapes, and results in a serious
degradation of capacity - as you are seeing here.


Best regards,

Wolfgang Denk

--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de
Living on Earth may be expensive, but it includes an annual free trip
around the Sun.

[Frank Cherry]

My storage daemon hardware:

Microsemi Adaptec HBA 1100 4i - Speicher-Controller - 4 Sender/Kanal - SATA 6Gb/s / SAS 12Gb/s Low Profile - 1.2 GBps
Quantum LTO-7 HH - Bandlaufwerk - LTO Ultrium (6 TB / 15 TB) - Ultrium 7 - SAS-2 - intern
A separate Seagate IronWolf NAS HDD 4TB, SATA 6Gb/s (ST4000VN008) is used for spooling partition only.

The SATA HDD is plugged on the main board's SATA Port. 300 MB/s = 2,4 Gb/s, so the 6 Gb/s should be OK.
Taking a look to the last job: Despooling elapsed time = 03:13:27, Transfer rate = 99.29 M Bytes/second

Maybe a solution to plug the HDD directly to the SAS controller?

Thanks for help Wolfgang,
Frank

[Frank Cherry]

Okay, checking the datasheet of the HDD, the max. cont. data rate is 180 MB/s, that's the bottle neck.

I will replace it with a SAS HDD, plugged directly to the HBA.

Wolfgang, can you explain please the context between start-stop mode and the serious
degradation of capacity?

Thanks, Frank

[Wolfgang Denk]

Dear Frank,

In message <8a1afda1-c38f-4411...@googlegroups.com> you wrote:
>
> Okay, checking the datasheet of the HDD, the max. cont. data rate is 180
> MB/s, that's the bottle neck.
> I will replace it with a SAS HDD, plugged directly to the HBA.

Are you sure this will be sufficient?

I see for example: "HP SAS 15K SFF Hard drives offer sustained
performance of 260 MB/s to 175 MB/s (outer to inner diameter)."

this would still be too slow. Either you set up a RAID array, or
you go for SSD for spool data.

> Wolfgang, can you explain please the context between start-stop mode and
> the serious
> degradation of capacity?

Sorry, I don;t have any reliable data here. Modern LTO drives can do
"speed matching" (i. e. slow down tape motion for slower incoming
data rates), but only within certain limits. Just listen to your
drive when running a backup - you can hear easily when it's runnin
slower, and when it stops completely.

I don't have any documents / specs that allow to estimate the impact
on total storage capacity, sorry.

Best regards,

Wolfgang Denk

--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: w...@denx.de

I can't say I've ever been lost, but I was bewildered once for three
days. - Daniel Boone (Attributed)

[Frank Cherry]

Thanks Wolfgang,
I have also read some SAS datasheets of HDD's and 300 MB/s are whishes. So RAID or SSD like you wrote are the solutions.
My plan is now to buy excatly the same HDD for spooling and setup a softraid 0 (stripe set).
There should be theroretically 2x180 MB/s = 360 possible, because there is only one file which is used when spooling for the backup job is enabled.

Frank