Tape Backup performance issue with a PE2950 with MD1000 RAID 5arrays attached via Perc5/e controller.

[Gary Mansell]

Hi,

My company has a Dell PE2950 with 1 tray of MD1000 300GB SAS drives in
RAID5 (3.5TB) and 1 tray of 750GB SATA drives in RAID 5 (9TB). They are
both attached via a Perc5/e SAS controller card. All volumes are
configured with LVM2 partitions and ext3 filesystems. We backup this
data with an Overland Neo200 with 2x LTO3 tape drives attached to the
server with a dual ported LSI ultra 320 SCSI card and Netbackup
Software.

We generally get a backup performance of about 35MB/s. This equates to
about 50 hours with two drives and is hence our entire weekend backup
window.

My first question is that this seems rather slow: the reason that I say
this is that a noddy dd read test to /dev/null shows a raw sequential
read speed from the MD1000 arrays of about 200MB/s. Now I realise that
this is bypassing the ext3 filesystem to an extent but there seems to be
quite a discrepancy here. The only other things that I can think of that
might be affecting this is disk fragmentation on the filesystems. Is
this to be expected, what speeds do others of you get from similar
configurations? Where is the bottleneck likely to be here as the LTO 3
tape drives are quoted as 54-160MB/s with compression!!!

We are looking to expand this storage capacity by adding another MD1000
of 1TB SATA drives in RAID5 (13TB). This will either daisy chain off of
one of the above tray's Perc5/e channels (not great for performance),
or, if we chose to move the backup system to a separate dedicated
server, we can use the freed SCSI card slot for another dedicated
Perc/5e SAS controller. The problem that I see with this is that I feel
that the backup performance will degrade if the server is backed up over
the network rather than locally. Is this likely?

We could install LTO4 tape drives in our Neo200 as they are rated with
50% faster performance of LTO3 but I am concerned that as we are not
hitting the performance limits of the existing LTO3 drives, we may see
no faster performance.

I would really appreciate people's comments on my configuration and
recommendations as to what the best solution would be to increase my
storage 200% but still to be able to back it up over a weekend.

Best Regards

Gary Mansell



 
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