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I have Dell EqualLogic PS5000E iSCSI Array. I have connected this SAN in servers directly. I used Jumbo Frames. In this case, everything is ok. My storage is ~25TB. Now, I need to choose, which RAID level I have to use. SAN proposes only 3 levels: 6, 50, 10. I have 16 HDD-s with ~1.8TB per each disk.

Which RAID level can you advise for virtualization and for work with databases?
Also, better to configure two raid levels. But SAN creates only one default storage pool with all our disks. If you know another way to configure two arrays, it will very nice

  • Do you have any sensible caching? I use Raid 6, but I have terabytes of cache (3.2 tb cache per 12tb of discs) which is also write cache (super fast ssd) – TomTom Feb 5 '19 at 7:32
  • @TomTom no, there are SATA disks – Piduna Feb 5 '19 at 7:37
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    THen you pretty much MUST use Raid 10, period. Years ago I was running a Raid 10 of 10k sata discs and I was running out of IO budget and thigns got slow even though I was using only 300gb discs (Velociraptors). Your jumbo frames are useless (couple of percent gains) given how extremely low your IO budget is going to be even with Raid 10. – TomTom Feb 5 '19 at 7:43
  • I confirm RAID-10 with a Equalogic SAN, I managed over 10 and always used that one for them. RAID-50 is easy to crash (I lived a RAID-50 crash on a Equalogic, so yes it happen) and it's not recommanded by Dell for production use. – yagmoth555 Feb 5 '19 at 21:03
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The PS5000 is a 16-disk system. It looks like you have 2TB drives (~1.82 TiB) based on the numbers you provided.

Dell's documentation on choosing RAID policy states that according to "best practices", RAID50 should not be used for 7.2K disks larger than 1TB, and RAID5 avoided completely, when storing business-critical data.

A single "member" (enclosure) can only be configured with one RAID policy, and cannot be split into 2 separate levels. Implementing multiple RAID types is accomplished on EQL systems via multiple members/arrays stored in separate "pools".

RAID10 would be my suggestion for database workload, but that may not provide adequate usable capacity depending on the size of your VMs. If the virtualization and database workload/size already "exist" on some other storage, it may be wise to look into some numbers there (e.g. read/write ratio, average and "peak" IOPS, total capacity/size, etc).

RAID6 provides miserable performance for write-intensive workloads, so I'd suggest avoiding it unless the vast majority of your IO is made up of reads. That number of drives in RAID6 could theoretically sustain 1500 IOPS with 100% reads (with one hot spare, 8K random IO), but 30% writes cuts that to below 600.

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The RAID level depend of many things but as common advise:

  • For virtualization use RAID6. Of course RAID6 is relatively slow (compared to other levels) but it offer possibility to have two disks failed and still have the data.

  • For database the wise array is RAID10. This will give you redundancy and very good disk speed (which is one of the possible bottlenecks for databases)

About Del EqualLogic - I have no experience with this product, but when create pool have you try (before creating RAID) to remove some disks from the pool? And later add them to another pool?

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I recommend using RAID-10 for Virtualization because of faster performance, best reliability, and redundancy. As for RAID-6 it's main advantage is protection of failures but you will take a hit when it comes to performance.

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