"RAID Policy" —— Dell发布的主要针对EQL61x0产品的技术文档

TiGi

本帖最后由 TiGi 于 7-26-2012 06:49 编辑
When a drive in a RAID set fails, an array behaves as follows:
If a spare drive is available: The spare automatically replaces the failed drive. Data from the failed drive is reconstructed on the spare and continues to be available. During reconstruction, the set that contains the failed drive is temporarily degraded. After reconstruction, performance returns to normal.
If no spare drive is available: Data continues to be available, but the set is degraded.
If another drive fails in a degraded RAID 10, RAID 5, or RAID 50 set: The member might be set offline, and any volumes and snapshots that have data located on the member are also set offline.
If another drive fails in a degraded RAID 6 set: The member is not set offline but continues to be degraded until the failed drives are replaced. Data is reconstructed on the replacement drives. If the first reconstruction is still underway, performance can be further reduced. After both drives are reconstructed, performance returns to normal.
When you replace a failed drive:
If a spare drive was used: Data has already been reconstructed on the spare drive, so the new drive becomes a spare.
If a set is degraded: Data is reconstructed on the new drive and after reconstruction, performance returns to normal.

seanlaser

很普通啊 没有什么新的内容啊

TiGi

本帖最后由 TiGi 于 7-26-2012 06:54 编辑
确实很普通。
不知道为啥，昨天上传的附件看不到。汗！因为我收V币的关系？？？
里面有段注释挺耐人寻味的：
Note: It is Dell’s recommendation that Dell EqualLogic arrays populated with SATA or NL SAS drives 1TB or larger be configured using a RAID 6 policy. RAID 6 minimizes the risk of data loss due to a multi-drive failure during a RAID reconstruction thereby maximizing protection of the RAID set. Therefore, this recommendation is strongly encouraged for ALL customers when choosing a RAID policy for their arrays.
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估计原因如下：
采用SATA/NL SAS磁盘的话，一般配置的容量会比较大，RAID组Rebuild所需的时间会更长一些（PS4100E 3T满配，RAID6完成初始化需要3x小时！！！），此外SATA/NL SAS磁盘的性能、可靠性也相对SAS而言稍许差一些。

seanlaser

RAID 6的性能貌似没有RAID5的好，而且丢1块同样性能下降很厉害。所以我现在通常只选RAID5+热备

TiGi

本帖最后由 TiGi 于 7-26-2012 18:40 编辑
硬盘数到一定程度之后（例如8个硬盘的RAID5和RAID6）差距就会逐步“缩小”（“7个和6个”的差距肯定要小于“3个和2个”）。
我怕死。所以RAID6、热备、冷备一起来。呵呵。

24242625

NL SAS 不等于SATA这主要是控制芯片上的差距

TiGi

本帖最后由 TiGi 于 7-26-2012 20:46 编辑
SATA是SAS的一个子集。
                    SATA      SAS
Duplex          Half          Full
ftp://ftp.compaq.com/pub/product ... res/sata-vs-sas.pdf
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不管LS或者其他怎样认为，对于个人而言，个人认为“NL SAS”更接近于“SATA”(当然，“NL SAS”不等于“SATA”)。
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随便Google了一下：
http://www.techrepublic.com/blog ... -disks-compare/5323
NL-SAS
NL-SAS is a relative newcomer to the storage game, but if you understand SATA and SAS, you already know everything you need to know about NL-SAS. You see, NL-SAS is basically a merging of a SATA disk with a SAS connector. From Wikipedia: “NL-SAS drives are enterprise SATA drives with a SAS interface, head, media, and rotational speed of traditional enterprise-class SATA drives with the fully capable SAS interface typical for classic SAS drives.”
There are two items of import in that sentence: “enterprise SATA drives” and “fully capable SAS interface”. In short, an NL-SAS disk is a bunch of spinning SATA platters with the native command set of SAS. While these disks will never perform as well as SAS thanks to their lower rotational rate, they do provide all of the enterprise features that come with SAS, including enterprise command queuing, concurrent data channels, and multiple host support.
    Enterprise/tagged command queuing. Simultaneously coordinates multiple sets of storage instructions by reordering them at the storage controller level so that they’re delivered to the disk in an efficient way.
    Concurrent data channels. SAS includes multiple full-duplex data channels, which provides for faster throughout of data.
    Multiple host support. A single SAS disk can be controlled by multiple hosts without need of an expander.
However, on the reliability spectrum, don’t be fooled by the acronym “SAS” appearing in the product name. NL-SAS disks have the same reliability metrics as SATA disks - BER of 1 in 10^15 and MTBF of 1.2 million hours. So, if you’re thinking of buying NL-SAS disks because SAS disks have better reliability than SATA disks, rethink. If reliability is job #1, then NL-SAS is not your answer.
On the performance scale, NL-SAS won’t be much better than SATA, either. Given their SATA underpinning, NL-SAS disks rotate at speeds of 7200 RPM… the same as most SATA disks, although there are some SATA drives that operate at 10K RPM.
It seems like there’s not much benefit to the NL-SAS story. However, bear in mind that this is a SATA disk with a SAS interface and, with that interface comes a number of benefits, some of which I briefly mentioned earlier. These features allow manufacturers to significantly simplify their products.

seanlaser

NLSAS的确盘体就是SATA，不过接口是SAS而已。不过最重要的区别在于，NLSAS通常各家供应商都有一定的质保维护服务，而SATA就悲剧的多了。就拿Dell而言，NLSAS通常和服务器是一样的，就是服务器如果3年保，盘也是3年，但SATA就只有1年而且不延保！！这个差别就很大了。

seanlaser

你冷备盘怎么做？现场备件存储么？备件本身的可用性如何保证呢？

TiGi

本帖最后由 TiGi 于 7-26-2012 21:53 编辑
冷备分两种：
一种是买设备的时候，要求加一个（当然是作为配件下单，价格应该会比整机里面的要贵）；
还有一种，是随后购买，当初的CX300就是这样，在标配的五个之外，买了11个。
冷备，并不能保证百分百完好 —— 但是通常硬盘插上去之后，能否上线是很快就能知晓的 —— 能够上线，我会邮件报修（我有金牌服务的邮件地址）并要求工作日的工作时段来换部件；如果不能上线，那就按照金牌服务等部件到场。
原本，设备都在公司的机房内，因此冷备盘，一般放在防静电袋中/塑料袋中，然后放在出厂递送时的包装内（一般是透明塑料盒、泡沫、纸箱），然后再放在铁柜内。
最近有个PS4100E要送到电信机房内，冷备盘还是放在公司内 —— 发现问题了，找人过去，先换掉。在公司/让公司前台等替换的备件，总比等备件到了再去电信机房或者在电信机房等备件要好。

TiGi

Dell服务器上配置SATA只有一年保？？？这倒第一次知道。
台机/笔记本上好像没有SATA只保一年的说法，反正我的台机/笔记本，只要保内硬盘故障都换的。

seanlaser

本帖最后由 seanlaser 于 7-26-2012 22:18 编辑
这个这几年才有的新规，现在你在线下单如果选了SATA盘，就会额外多附加个SATA的特别注意事项，就是说明保修只有1年这事。据说主要是前些年，有不少客户买了SATA盘做RAID，毁了一批又一批。Dell估计是觉得太亏了。
笔记本和台机没有NL-SAS可选，而且你不会当RAID用，能毁几个呢？

TiGi

配置SATA的服务器，一般都是最低配。这样的服务器，Dell的利润率肯定不高的。时间长了，Dell确实会觉得亏本。呵呵。