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Windows Thread, Planning exchange store and RAID redundancy in Technical; Hi folks Got a quick question. I am about to setup a new RAID 5 array and plan to to ...
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    Planning exchange store and RAID redundancy

    Hi folks

    Got a quick question.

    I am about to setup a new RAID 5 array and plan to to use this array for our exchange 2003 store and DFS. Some admins have said RAID 5 isn't suggested and I am better of using RAID 1.

    The server used to have a RAID 5 and we only used it for DFS and for this it was fine, but I also need more storage for emails so also plan to move the store onto this new array.

    I was just wondering if I could get peoples opinions on this

    Your help is appreciated

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    Re: Planning exchange store and RAID redundancy

    If you have a proper hardware RAID controller capable of RAID 5 then use that. Otherwise you might find that RAID 1 offers better performance.

    --
    David Hicks

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    zag
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    Re: Planning exchange store and RAID redundancy

    I've said this before but personally I would use 2 single drives, one for the OS and exchange program files, and another for the exchange store. If you run the best practices wizard on the 2007 setup cd it will tell you how to optimise exchange 2003 for the best possible performance which can do wonders.

    In my opinion raid is nice in certain situations but can often cause more problems than its worth in other situations. Especially in mission critical applications such as email where large databases are involved.

    I just don't think the performance gain justifies the added problems with raid going wrong and the difficulties of restoring raid volumes if corruption happens. A good backup strategy is all that is really needed and optimised exchange store.

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    Re: Planning exchange store and RAID redundancy

    Our exchange server is a HP DL380 with 6x72GB drives. This is divided so there are 2xdrives in RAID1 for the OS and Exchange program files, and 4xdrives in RAID5 for the data storage. This works well for us, and provides us with good performance and plenty of space.

    It's all down to how much space you require for you database to expand into. RAID 5 generally requires a minimum 3 drives to implement, so if you only require the amount of space on 1 Drive (say 72GB) then setting up 2 drives in RAID1 to give you 72GB total storage will give you a small improvement in performance over 3 Drives in RAID5 giving you 140GBish of space.

    If you're just using 2 drives, and are pretty sure you'll never expand the storage, then 2 drives in RAID1 will be better performance than a 2 drive RAID 5 array (if you controller even supports a 2 drive RAID 5 array, which is possible but not on all RAID controllers.)

    Personally I'd disagree with the above, RAID is an absolute must on all essential servers, as it ensures an un-interupted service should a drive fail. We have a lot of servers here (12 in total) and in total those servers have over 50 drives between them. On average 1 drive every couple of months fails on us, but every time the RAID setup keeps the system going. Remember with hard drives, it's a case of when they fail, not if. Because they are mechanical, they will fail eventually.

    Imagine the amount of downtime on our system if I had to restore data from our backup on each of these ocassions, not to mention the amount of time that would take. RAID allows operations to carry on as normal, slot a new drive into the array (we keep spares on site) the array is rebuilt and end users are none the wiser!

    A good backup stratergy is a must still, RAID is not a replacement for this, merely an extra level of protection.

    Mike.

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    Re: Planning exchange store and RAID redundancy

    I completly agree Mike. RAID is a must to keep your users happy with the IT network.

    RAID is a godsend for us it guys.

    I decided in the end to use RAID1 as where the current store lies, its on RAID 1 and it seems fine. I have used two huge 750gb WD RE2 enterprise drives and decided to use RAID 1 in the end.

    I think we be ok.

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    Re: Planning exchange store and RAID redundancy

    With drives of that size, that was probably the most sensible decision. All our servers are HP Proliant, they take SCSI drives which are more limited in capacity, hence we use RAID 5 a lot to produce larger drives.

    Our 12 Drive storage array on the other hand uses SATA drives, and is populated with 9x250GB drives. This runs RAID6 with a hot spare so the capacity is about 1.6TB (taking no chances with this, as it stores 90% of our network data, and would be absolutly catastrophic if we lost it even for a few hours.)

    I have lost a server before due to having no RAID setup and a drive failing. Once you've made that mistake once and delt with the hours of work restoring a server from a backup, you don't want to do it again in a hurry!

    I also know of a network admin who lost his job over not having RAID on the servers he setup, because 'he wasn't fufilling his job role by ensuring the integrity of the systems he was looking after.' Sounds a bit harsh, but the school systems were down for 2 days when his server drive failed and it caused a lot of disruption. He knew of RAID, but didn't use it.

    When it emerged to the Senior Team that a relatively easy to implement system like this would have prevented the whole disaster, they said he was neglegent in his job role, and that was that.

    Mike.

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    Re: Planning exchange store and RAID redundancy

    Quote Originally Posted by maniac
    With drives of that size, that was probably the most sensible decision. All our servers are HP Proliant, they take SCSI drives which are more limited in capacity, hence we use RAID 5 a lot to produce larger drives.

    Our 12 Drive storage array on the other hand uses SATA drives, and is populated with 9x250GB drives. This runs RAID6 with a hot spare so the capacity is about 1.6TB (taking no chances with this, as it stores 90% of our network data, and would be absolutly catastrophic if we lost it even for a few hours.)

    I have lost a server before due to having no RAID setup and a drive failing. Once you've made that mistake once and delt with the hours of work restoring a server from a backup, you don't want to do it again in a hurry!

    I also know of a network admin who lost his job over not having RAID on the servers he setup, because 'he wasn't fufilling his job role by ensuring the integrity of the systems he was looking after.' Sounds a bit harsh, but the school systems were down for 2 days when his server drive failed and it caused a lot of disruption. He knew of RAID, but didn't use it.

    When it emerged to the Senior Team that a relatively easy to implement system like this would have prevented the whole disaster, they said he was neglegent in his job role, and that was that.

    Mike.
    raid 6 eh, that's the best raid scheme combining efficient use of storage, performance and reliability....been used by Netapp filers for years in the form RAID-DP, out of interest which array are you using ?

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    Re: Planning exchange store and RAID redundancy

    Quote Originally Posted by ittech
    I've said this before but personally I would use 2 single drives, one for the OS and exchange program files, and another for the exchange store. If you run the best practices wizard on the 2007 setup cd it will tell you how to optimise exchange 2003 for the best possible performance which can do wonders.

    In my opinion raid is nice in certain situations but can often cause more problems than its worth in other situations. Especially in mission critical applications such as email where large databases are involved.

    I just don't think the performance gain justifies the added problems with raid going wrong and the difficulties of restoring raid volumes if corruption happens. A good backup strategy is all that is really needed and optimised exchange store.
    hmmm, that's an interesting viewpoint but i don't think i agree entirely. I do agree that a backup stategy is vital, and that to rely on RAID and forgo a good backup policy is a recipe for disaster.

    but surely there's not just a performance gain from implementing a raid set, the added benefit of raid 6 for instantce.. which will tolerate two drive failures and a hot spare that allow raid sets to be rebuilt on the fly using the spare drive with no downtime. That is the essense of mission critical, and a single drive just doesn't cut it, corruption of data and hardware failure is just as much a risk with one drive, if not more so.

    I personally think optimum Exchange fault tolerance and performance requires an external storage shelf, whether that means SAN or DAS depends on you're budget. If you're going down the iscsi san route you really should look into exchange clustering. By default in the enterprise anything mission critical is connected to SAN storage.

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    zag
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    Re: Planning exchange store and RAID redundancy

    I would argue that the reason you are having drives fail is because you are using so many drives in the raid set-up therefore increasing substantially the risk of failure.

    I do use raid5 on my main file server and it works very well, but for exchange or domain controllers I stick with the non redundant way of doing things. Backupexec does a 1 click restore of exchange that works really well in disaster situations, I would much rather do that than wait 9hrs for a raid drive to repair itself

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    Re: Planning exchange store and RAID redundancy

    Quote Originally Posted by ittech
    I would argue that the reason you are having drives fail is because you are using so many drives in the raid set-up therefore increasing substantially the risk of failure.

    I do use raid5 on my main file server and it works very well, but for exchange or domain controllers I stick with the non redundant way of doing things. Backupexec does a 1 click restore of exchange that works really well in disaster situations, I would much rather do that than wait 9hrs for a raid drive to repair itself
    This is where the difference between a proper external storage array and internal RAID cards make all the difference. On good FC or iSCSI arrays,
    disks can still be written too while a rebuild is taking place, these arrays offer zero downtime and no waiting around, that's why an FC storage arrays cost so much more than servers with internal storage. Plus good arrays will have dual redundant controllers and a minimum 512MB of cache per controller!!!!!

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    Re: Planning exchange store and RAID redundancy

    On this topic, I understand that RAID 6 has a performance hit compared to RAID 5, which intuitively makes some sense. With that in mind, is it not better to have RAID 5 + hot spare than RAID 6, especially as the hot spare isn't being used so isn't getting the wear and tear of its RAID 6 counterpart.

    As far as I can see, the only advantage of RAID 6 is that it can have exactly 2 disk failures in quick succession whereas a 2nd failure within a few hours on 5+Spare would lose your data. If you're looking at (say) a 10 disk array, the odds of *exactly* 2 disks failing within a few hours seem fairly slim.

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    Re: Planning exchange store and RAID redundancy

    True, the odds are low, but it was the peace of mind knowing the array was going to have 9 drives in it, so the likelyhood of losing it is greater. Over periods like christmas, the school is un-manned for almost 2 weeks, so there is a chance however small, that this scenario could occur. With this storage array we were taking no chances. We've had no performance problems from it so far, always seems to work 100% reliably, and we're very happy with it, even if it seems like overkill to some. The SATA drives are cheap enough, so we don't feel too bad shrinking the capacity to allow for that much redundancy.

    Most of our RAID 5 arrays consist of just 4 drives, and the reason we have so many drive failures is because a fair number of our servers are getting to 4 years old now, but they still function OK in their roles, and the RAID setups mean we can still rely on them. We've not had a drive failure in our main array yet, this is only 15 months old.

    @ittech remember the RAID array can still serve data while it's rebuilt, so there's no downtime.

    @torledo I can't remember the exact model of the array we have, it's from HP storage works, will hold 12 SATA drives (currently populated with 9) and links to the host server by SCSI. The host server for it is running Windows Storage Server. It's been exceedingly reliable so far, and it was well worth the investment.

    Mike.

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    Re: Planning exchange store and RAID redundancy

    Quote Originally Posted by sahmeepee
    On this topic, I understand that RAID 6 has a performance hit compared to RAID 5, which intuitively makes some sense. With that in mind, is it not better to have RAID 5 + hot spare than RAID 6, especially as the hot spare isn't being used so isn't getting the wear and tear of its RAID 6 counterpart.

    As far as I can see, the only advantage of RAID 6 is that it can have exactly 2 disk failures in quick succession whereas a 2nd failure within a few hours on 5+Spare would lose your data. If you're looking at (say) a 10 disk array, the odds of *exactly* 2 disks failing within a few hours seem fairly slim.
    Yes, you're right there is a performance penalty for using RAID 6, with hitachi tagmastore arrays it can be up to 33% on random write operations. Sequential writes take a 15-20% performance hit and, as you'd expect, there is no performance penalty for read operations.

    But it's not as cut and dried as that, the performance hit varies between vendors depending on how they've implemented the RAID 6 algorithm in their controllers. For that reason the likes of EMC and Engenio based arrays don't support RAID 6 as of yet. It hasn't hit prime time yet.

    Performance isn't the only criteria, the main advantage of RAID 6 is that you can defer the rebuild in the event of a single disk failure to a time that suits you. With RAID 5 you have no choice but to rebuild the array,
    and with the current relatively slow and massive SATA drives (slow compared to FC) those many many hours rebuild time pose a big risk...so if a second disk fails during that period you're stuffed...and unplanned downtime is then required for restoring from tape backup. Although unlikely it has been known to happen.

    Is RAID 6 for the very paraniod ? Yes it is, but it's also for those who absolutely cannot tolerate any significant downtime.

    One of the companies who've had runaway success with RAID 6 is netapp.
    They're variant raid scheme called RAID-DP (stands for dual parity) has virtually no performance hit compared to RAID 5...they've managed this in part thanks to additional whizz bang technologies in their array controllers.
    And guess who dominates the mid-market for Exchange and SQL NAS storage....you've guessed it, Netapp.

    If you can't afford a Netapp filer, or need greater performance than offered by RAID 5, then there's always RAID 10. RAID 10 has always had the problem of the terrible waste of RAW diskspace. With the low price of modern SATA drives that's no longer such an issue if you don't mind having a no more than 50% of you're RAW capacity available to you.

    RAID 1 for OS,
    RAID 5 for SQL and exchane type apps, and
    RAID 10 for high performance apps

    ....are pretty much all you'll need, using RAID 6 for you're exchange store using internal RAID SAS/SCSI controllers will probably end in tears...so stick to RAID 5 for internal storage.

    ....but expect RAID 6 to have a big impact once the storage array vendors tackle the performance problem in the way NetApp have done. You'll probably never see comparable performance between RAID5 and RAID6 on internal controllers from the likes of Adaptec, but the array based controllers from hitachi should improve and catch up to RAID 5, and expect EMC to enter the market at some stage. At the end of the day it's the business customers who are demanding this extra level of protection.

    And they drive what vendors put in their products, if schools don't need it or don't understand it then they shouldn't use it.

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