With almost certainty, a mirrored configuration should out perform a raid-5
configuration. Especially where a write intensive application is involved
(like an ADSM Server). You always have to perform additional I/O with
raid-5 to read parity data and write new parity data. This is even more
evident  in hardware that does not have large amounts of write cache. This
is normally the case with internal server raid devices since these systems
do not usually have built in battery backed up cache memory for insuring
data integrity in the event of a failure.

 We are able to notice a write penalty even on our HDS 7700 DASD subsystems
running on our OS/390 systems. We have one subsystem that has 4gb of cache
and we have measured backing up a full 3390-3 (2.8gb) in 6 minutes with a
restore of the same volume taking 8 minutes (and these devices have
extensive cache algorithms to minimize the write penalty).

 Also I had incorrectly stated before that we saw a 33% improvement in V2
under NT when we changed from raid-5,  but the actual numbers were we went
from 1gb hour throughput to 1.5gb hour which would be a 50% improvement.
This was the only change made during that time.

RAID-1 (mirroring) has almost zero overhead when compared to native disk
devices. The difference is almost un-measurable But the trade off is you
need twice the disk. That is why we mirror the important files like NT,
ADSM DB & recovery log and use native disk for storage pools. If we have a
failure on a storage pool device (which has not happened yet) then we will
just discard the data and it should be picked up on the next backup.

Hope this helps.




bill AT NSMC.PARTNERS DOT ORG on 01/26/98 08:51:00 AM

Please respond to ADSM-L AT VM.MARIST DOT EDU

To:   ADSM-L AT VM.MARIST DOT EDU
cc:    (bcc: Mike Wilson/Texas Utilities)
Subject:  Re: ADSM V3 on NT




>010Date: 23-Jan-98 14:40:56 -0600
>From: MWILSON6 @ SMTP (Mike Wilson) {mwilson6 AT TUELECTRIC DOT COM}
>To: ADSM-L @ SMTP {ADSM-L AT VM.MARIST DOT EDU}
>001Subject: Re: ADSM V3 on NT
>
>We have implemented ADSM Version 3 on NT. We do not have anywhere near
1000
>clients, but the clients we do have are fairly large file servers with
>approximately 1 terrabyte total  disk space. The nightly change rate is
>around 40gb and sometimes hits 80 gb per night. On a typical night,
backups
>start around  6pm and complete by 3am. We have moved some of the clients
to
>a dedicated 100 megabit Ethernet network, but most of the data is
currently
>being moved across 16 megabit Token Ring. We tried ADSM/NT 2.1 on the same
>hardware, but it could not get any where near this throughput, when we
went
>to V3 we saw a 300% performance improvement. We also had taken  the sever
>disk out of its raid 5 configuration and saw a 33% improvement (this was
>done while under V2 before we went to V3). NT and the ADSM database run on
>raid 1 mirrored disk and the storage pools are native non-fault-tolerent
>disk. Our storage pools  are 52gb. All other functions like expiration,
>migration and reclamation are running on a timely basis. At last count
>these clients contained over 2.5 million files, but most of the nightly
>changed data is from large database files.
>
>Server hardware:
>IBM 704
>2 200mhz Pentium Pro
>256 meg memory
>2 4.5gb raid1 hard disk (operating system)
>2 9gb raid1 hard disk (db & recovery log)
>6 9gb unprotected disk (stg pools)
>
>STK 9714
>100 slots
>4 DLT7000 tape drives
>
>
>
>
>
>BOIREER AT EUROMSX.GEMSE DOT FR on 01/23/98 11:39:57 AM
>
>Please respond to ADSM-L AT VM.MARIST DOT EDU
>
>To:   ADSM-L AT VM.MARIST DOT EDU
>cc:    (bcc: Mike Wilson/Texas Utilities)
>Subject:  ADSM V3 on NT
>
>
>
>
>Hello,
>Has anybody already implemented ADSM V3 NT with more than 1000 clients.
>If so, what type of server are you using?
>We are planning to implement this solution with 1800 PC client on a HP
>LxPro Bi-PentiumPro 200 with 256MB of RAM and 50GB of Disk (Raid 5)
>connected to a StorageTek 9714 (100xDLT7000) library. We are wondering
>if NT can handle this.
>Thanks.
>
>> g          GE Medical Systems
>> __________________________________
>> Eric Boireau                                                GITS
>> Unix / NT  System Engineer
>>
>> GE Medical Systems S.A
>> 283, rue de la Mini?re
>> 78533 BUC Cedex France
>> T?l: (33) 01 30 70 39 51,  DC: 8*644 3951
>> Fax: (33) 01 30 70 39 20, DC: 8*644 3920
>> mailto:boireer AT euromsx.gemse DOT fr
>>
>> Salutations / Best Regards
>>
>>
>>
Is a mirrored configuration better / faster  than a raid 5 environment?