Rod,
After spending 4 weeks using file device class disk pools, I would say
use random access. Here is why:
The speed of the random access disk pools is phenomenally better than
the file device class - not sure why though
The volumes (from the presentation I just read from the other email)
are supposed to be picked based on filesystems with no volume mounted.
What I found is the it selects them in collation order. This accessed
the volumes on one raid group, giving the worst performance of all.
After using a kludgy method to spread the data around, the performance
was better, but did not approach random access
Small files were a problem in some cases. Since I was collocating, if
alot of small files were written to a volume (in this case, it was
moving my dirmc pool), there can be alot of wasted space. Apparently,
a block of 256K is written to disk no matter how much data is being
written. If alot of small files are written to a volume, space can be
wasted because the volume will fill before capacity is reached (we were
using predefined volumes)
It takes alot of time to predefine the volumes. We were finding it
took about 19 hours to predefine 2TB. We were able to run 8 of those,
so it ended up taking 19 hours to predefine 16TB, but that is still a
long time.
Some portion of space is taken up by volumes that are not yet full
(with predefined volumes at least) in a file device class. This is not
a worry with random access, but fragmented aggregates could be a worry.
My plan is to move data off of random access volumes on the weekends to
help prevent fragmentation.
If you have any other questions, please let me know.
--- "Park, Rod" <rod.park AT TYSON DOT COM> wrote:
> Let me ask again because I didn't get much feedback. How do we find
> the
> thread limit, and can people weigh in on whether they use big disk
> pools
> (50TB-200TB). The advantages/disadvantages of big disk pools versus
> devclass=file any gotchas either way. We are looking at buy a lot
> more
> disk and creating big diskpools to land data on and be the primary
> pool
> instead of tape. Thank in advance.
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf
> Of
> Andy Huebner
> Sent: Monday, March 27, 2006 11:43 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Random Access Disk Pools
>
> We found the limit. There are some posts in this forum from the
> first
> of the year about the problem we ran into.
>
> Andy Huebner
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf
> Of
> Park, Rod
> Sent: Monday, March 27, 2006 6:45 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Random Access Disk Pools
>
> We use random access pools, how do you know what your thread limit
> is....we've never had any issues with ours but we're thinking about
> adding a lot more. What's the biggest reason you do/don't use
> devclass=file over disk storage pools....arguments either way?
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf
> Of
> Andy Huebner
> Sent: Friday, March 24, 2006 3:37 PM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Random Access Disk Pools
>
> Be careful with how many disk pool volumes you create. Each volume
> uses
> 1 thread, add this to all of the other threads in use, our TSM server
> would die at around 1800 active threads.
>
> Andy Huebner
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf
> Of
> Andrew Carlson
> Sent: Friday, March 24, 2006 11:04 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: [ADSM-L] Random Access Disk Pools
>
> I have heard in the past that random access disk pools can become
> fragmented and practically unusable after a while. I was wondering
> if anyone sees this in the real world? I posted the other day about
> managing predefined volumes in a file type devclass, and the only
> answer I got said they were using random access pools. I would MUCH
> rather have a random access pool, so if there is no problem with
> this, I will convert over to random access. Thanks for any input.
>
> TSM 5.3.2.3 on AIX 5.2.5 EMC Clarion Disk, 120 TB in 2TB LUN's
>
> Andy Carlson
>
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