Re: Optimal Disk Layout??

From: satar naghshineh <satarnag_at_yahoo.com>
Date: Fri, 21 Sep 2001 12:23:51 -0700
Message-ID: <F001.003952AB.20010921123030@fatcity.com>

Hi Walter,

It looks like you're having a bottleneck on your controller during a hot backup. This is a result of (1) reading the data then (2) writing the data and compressing the data within the same controller.

To answer your questions:
1. During RAID 5, all your disks are being written to and parity rotates on each disks. You can do a search on RAID levels on the web. One thing to note is that a RAID 5 needs at least 4 physical drives to work efficiently.

2. Since you are running a single A1000 with 8 slots, I would avoid the RAID 0+1 idea. Keep the RAID 5 setup unless you go with 10 drives, then go for RAID 1+0. Alocate a couple of drives for redo logs (on seperate internal disk bus within the A1000) and multiplex the redo logs on the two drives. Keep a drive for the archived redo logs, you can even use a bigger hard drive that has the same form factor as the 9GB hard drive. Try to squeeze a Hot Spare in as well. seperate the RAID 5 drives between the two internal disk bus of the A1000 as well. Look into backing up your database to a TAPE device instead of hard drives. With a 8GB database, you can restore your database in 10 minutes with a DLT 8000, just make sure the backup software binaries and database resides on a sperate system on your network.

Your best bet, if you can afford it, is to return the A1000 and get a A3500, which comes with 2 D1000's. Buy the additional controller for redundancy and do a RAID 50 or 10. This is the best bet because of the redundancy on the conntroller, disks and internal bus of the system. Also implement the TAPE backup system.

I believe the A1000 is a 10 slot (for 9GB drives and some 18GB drives). If it is only a 8 slot storage, make adjustments accordingly, keeping the internal disk bus in mind. Lay out your disk:

Slot 1 - RAID 5 DRIVE
Slot 2 - RAID 5 DRIVE
Slot 3 - Archived redo logs
Slot 4 - Redo Logs (Members A)
Slot 5 - EMPTY
Slot 6 - RAID 5 DRIVE
Slot 7 - RAID 5 DRIVE
Slot 8 - Redo Logs (Members B)
Slot 9 - HOT SPARE
Slot 10-  EMPTY

If it is a 10 slot and you decide to go with 10 hard drives, implement RAID 1+0 to increase write performance. Use the Hot SPARE disk as an extra disk to throw junk into.

Hope this helps. Let me know if I confused you more or if you need additional info.

Regards,
Satar

• Walter K <alden14004_at_yahoo.com> wrote:
  > Hi,
  >
  > I'm encuntering a relatively high iowait percentage
  > when my hot backups are running. The platform is Sun
  > (E420 2cpu running SunOS 5.7) with an A1000 disk
  > array
  > (8 9Gb drives, hardware Raid-5). The array is one
  > volume and all DB components (redo, archive, data,
  > index, system, etc.) are on the same volume except
  > for
  > the binaries. The database is not large, only ~8Gb
  > in
  > size and the transactional volume is not much
  > either.
  > However, when the backups run, the iowait according
  > to
  > 'top' hovers between 50-70% which causes our
  > application to time-out via Web Logic 6.0.
  >
  > The developers can't explain why the timeouts are
  > occurring (WLS 6.0 is a new upgrade from 5.1). The
  > SysAdmin isn't much help either.
  >
  > I have an opportunity to rebuild the database on
  > another machine and use RAID 1+0 -- the thought
  > being
  > that we are choking ourselves with Raid-5 when the
  > hot
  > backups are performing the cp's (copies) and then
  > the
  > files are compressed.
  >
  > My first question is, how is the data distributed
  > across the drives in my Raid-5 configuration? Is
  > each
  > disk being filled contiguously in series or is the
  > data being spread around in a pseudo-striping
  > manner?
  >
  > My second question/dilema is, the new array (another
  > A1000) will have 6 18Gb drives and with Raid 1+0
  > that
  > shrinks to 3 drives of usable space for everything
  > except redo and archive. 4 9Gb drives will be added
  > in
  > two mirrored sets, one for redo and the other for
  > archive. I'm afraid that I will see worse I/O
  > performance with the new array because it has so
  > fewer
  > physical drives, thus eliminating the benefit of not
  > having to write the parity info.
  >
  > Do you concur? Knowing the two arrays I have to work
  > with, which would be the better configuration?
  >
  > Any suggestions, recommendations would VERY much be
  > appreciated.
  >
  > Thanks again for the feedback.
  > -w
  >
  

  ---

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Author: satar naghshineh
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Received on Fri Sep 21 2001 - 14:23:51 CDT