Increase RAID sync rate


  • The HDDs are in an external USB case.
  • RAID5 with 3 HDD (10TB)
  • Software RAID5 with mdadm and Debian Linux

Adding a new disk

When you add a new HDD to an existing RAID, a sync is started. In my case I added a 10TB disk to a RAID5. The sync started and as estimated time I got something in the range of days. The estimated time is listed in finish=5384 min.

This number goes up and down a little bit, but overall result is that the sync will need days. After checking the status again after a while, it still showed days: finish=3437min.

The main problem here Is the rate at which mdadm can sync the data. The value is between 30000K and 43000K. That’s not much given the size of the RAID. There are several tips available on the internet. What help me was to set the stripe_cache_size.


You set the size of stripe_cache_size for each RAID device (mdX). In case your RAID is md0:

echo 32768 > /sys/block/md0/md/stripe_cache_size


The speed increased to 100000K/sec. That’s close to 3x faster than before. Time went down drastically.

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Personas 3 and IE11

“Personas 3 does not work with IE11.” I came across this lately at work and before others are having the same questions, I thought I`ll write a blog to help Personas 3 architects.

Key take away is that Personas 3 works with IE11, but currently is not supported. In general, Personas 3 “follows the Desktop Browser Support Statement as published in PAM for the NW 7.4 release”. [1] NW 7.4 supports IE11, so the goal is to have Personas 3 work flawless on IE11 too. There is a restriction mentioned in the SAP Note about that “IE11 is currently not supported“. Emphasis on currently. The real problem why IE11 is currently not supported is explained in [2]. IE11 has a huge performance problem that hits you when running Personas 3. This problem is not caused by SAP, but by IE11 and as the note states, “SAP has reported several issues to Microsoft on 04th of May 2015”. As of August 20th, Microsoft delivered a patch that looks to address the issue (“MS provided a new version of IE11 which dramatically improves the performance issue”). As the notes state, SAP is taking a look into this and when the patches provided by Microsoft are evaluated and considered good enough, SAP will update the note [1] and IE11 will be supported. For now we`ll have to wait and hope that this will be done early.

Important SAP Notes

[1] 2050838 – SAP Screen Personas – Limitations/Restrictions/Behavior

[2] 2163772 – IE Issue: Massive performance issues in IE11

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