RAID 1 or RAID 5

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Exchange 2003
RAID
RAID 1
RAID 5
SQL 2000
SQL Server 2003
I have 1 file server and 1 email server. both are Win2k3....one with exchange 2003 one with SQL 2000 but only 4 people using a small accounting program on it. Both are Dual XEON 2Ghz processors 1 Gb RAM 15K rpm hard drives. Ultra SCSI 160 controllers File server has software RAID 1, Exchange Server has hardware Raid 1 Both have 4 disks each=2 for system files-mirrored and 2 for data files-mirrored. I have plenty of drive space for my needs. approx. 80-90 users. My question: These servers are going into production in a few weeks. I prefer to use RAID 1 vs. RAID 5 because it is allowing me to keep spares on hand due to cost. What, if any, would be the downside of doing so vs RAID 5. If some say 'performance', is it really that significant with such little traffic on the servers? thanks in advance
ASKED: August 16, 2005  2:37 PM
UPDATED: August 28, 2008  8:35 PM

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If you have 4 disks why not do RAID 10. That’s a mirrored stripe-set. That is two RAID 0 (stripe) volumes configured in a RAID 1 (mirror). It gives you the speed of striping with the saftey of mirroring. I’ve got a couple of servers configured like that and it seemed noticably faster than RAID 5 though I never ran any bench marks.

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  • PaulHinsberg
    There is a significant performance impact to running RAID 5 over RAID 1. Cache on the card can help - but is not advisable in some instances (databases namely - and I would include Exchange in databases). RAID 10 (or RAID 0+1 as it is truly implemented in most cases), has the beneift of full redundancy as well as the speed of striping. Generally it is the best solution - although it tends to be the most costly. You RAID 1 configuration is better than a RAID 5, but it also depends on how the applications are dispersed amoung the drives. Here is an excerpt from a recent paper I wrote: When attempting to build a disk subsystem that performs as desired there are a few key concepts. These concepts are briefly described here to help understand the choices made for the Exchange disk configuration . Disk I/O consists of 4 operations: ? Random Reads ? Random Writes ? Sequential Reads ? Sequential Writes When considering the performance of a disk subsystem for an application you will need to know the type of operations that application performs. In most cases the application performs multiple types of these operations. Often, the application allows for the types of I/O to be divided. This is the case with Exchange. Exchange has the following: Exchange binaries ? Random Reads, usually stored on the C-drive with the OS. Exchange use of TEMP/TMP folders for SMTP storage ? Random Read/Write Exchange Log files (per storage group) ? Sequential Reads/Writes Exchange Database Files ? Random Reads/Writes These operations must also be balanced with the OS operations. Windows Binaries ? Random Reads Windows Page File ? Random writes and reads Ideally, you would separate each of the various I/O operations. Of course, there is storage space and money to consider. Separating the different disk I/O operations will cost more in drives and drive bay space. In order to achieve the best performance, you must also consider the fault tolerance method used. Table 2 ? RAID performance RAID Fault Tolerance Read Speed Write Speed 0 None Excellent Good 1 Yes Excellent Good 5 Yes Good Fair 0+1 Yes Excellent Excellent For unusually large volumes of data RAID 5 is typically employed. The fault tolerance is good and the efficient use of space is good. As far as I/O performance, RAID 5 is the worst of the bunch. Manufacturers use caching methods and I/O algorithms to help compensate. For superior performance and fault tolerance RAID 0+1, a combination of the striping and mirroring, is the best. Of course you will only get 50% of the overall raw capacity of the drives. However, with drive prices these days, it is typically a choice companies make.
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  • Bobkberg
    My $.02 worth... One factor I haven't seen mentioned yet is "Hot-Swapping" I've not seen RAID 1 configured for hot swapping (although I'd guess it's possible), although I've seen plenty of RAID 5 that have been designed hot or non-not swappable. To the best of my knowledge, RAID 0 is not swappable AT ALL, since it's just a performance booster. But - You also need to consider whether or not hot swapping is a necessary feature for you. If you don't have a "maintenance window" in which to take down a system to rebuild a failed disk, then you should look at hot-swappable systems only. Bob
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  • PaulHinsberg
    Actually almost any RAID controller card and Business Class server worth it's salt can hot-swap RAID 1 drives. Just as in any RAID 5 configuration there will be cycles spent on repopulating the drive with data, but it will recover in time.
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  • Ghigbee
    The only benefit to RAID-5 that I can see is that you get more usable drive space for the number of drives. RAID-1 requires one mirror drive for each drive in use, and RAID-5 requires 1 extra drive to allow space for parity information (The information is spread over all the drives however). I started moving towards RAID-1 for OS partitions and RAID-1 or RAID-10 for data. I mainly use RAID-10 for database servers that get a lot of traffic. That is my $.02.
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  • Kurthp
    Saw a reference to this doc on the askTom@oracle.com site. http://www.oracle.com/technology//deploy/availability/pdf/oow2000_sane.pdf Definitely lots of discussion on this topic. Hope this might provide some insight.
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  • Astronomer
    Given your description, RAID 1 sounds just fine. I would recommend building your mirrors with a hardware RAID card instead of doing it in software. Performance and reliability are better. Concerning the hot spare question: Back in 2000 I got my first adaptec card that would do an automatic rebuild using a hot spare. I configured a mirror with a hot spare and loaded NT 4.0 on it. During a demo for my manager, I pulled out drive 0 while booting NT and watched the boot slow down to half speed as the RAID card rebuilt the mirror. NT finished booting before the mirror was rebuilt but it didn't know anything had happened. This was enough to sell management on using these cards for all of the critical servers. I expect most brands now have this capability. rt
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  • Joelsplace
    I know we are talking SCSI here but I thought I would warn people about Maxtor drives connected to Promise RAID controllers. I have had at least 4 with numerous failures and only once did the failure not take out the other drive also. None of the Promise cards I've used were able to do a background rebuild either. I've had good luck with Silicon Image in that I've never had both drives fail or be corrupted at once and they do automatic rebuilds in *most* cases. Joel
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  • Astronomer
    Joel: Some instructors here tried promise SATA cards here with poor results. In IT we are using adaptec and 3ware cards. Other than one bad adaptec card out of the box, (which took months to get replaced), both brands of SATA cards have worked well for us. rt
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  • Poppaman2
    Sorry for my late entry into this discussion - I normally would have chimed right in, but spent the last two days dealing with a Zotob infection. To further explain the reason why RAID 5 is ofttimes reccomended over RAID 1: With large data sets, performance can be best optomized if the data is spread over a large/larger number of spindles (ie: more drives). There is also the block size issue to consider (larger (128K +) vs. small (as small as 16K). It's a rather esoteric subject, and why storage analysts have a tendancy to bring down the big bucks.... For your purposes, and provided your database is not overly large (200Gb +/- as a rather arbitrary figure), using RAID 0+1 would most likely be your best bet. Once you start to get into larger (500+ GB) datasets, using RAID 5 allows spreading the data over multiple spindles while retaining reliability (hot spare drives in case of failure...). Consider setting up your servers with two volumes: the O/S and applications on a RAID 1 (or 0+1) volume and your data on RAID 5. The cost of hardware of course goes up the more drives you utilize, but with multiple 10K or 15K RPM drives of a smaller size (73GB as opposed to 146GB or larger) you will achieve an excellent balance of reliability and performance. PaulR. GSEC (Security), ACSP (Storage)
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  • Guardian
    Hot Swap or Spares Still both in RAID 1 (Mirror) and RAID 5 if there's a disk failure, data availability is reduced immediately. Also I/O performance degrades while data recovery takes place (which it recovers after the hot swap or spare is online) I hope you have your disks configured to RAID 10 (that is different bus) Regards Newton
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