我有一个多年前创建的内核，在solr6.x上正确运行。
我已经把solr升级到7.7.3了。我已经启动了indexupgrade脚本：

/opt/solr/server/solr-webapp/webapp/WEB-INF/lib$ sudo java -cp lucene-core-7.7.3.jar:lucene-backward-codecs-7.7.3.jar org.apache.lucene.index.IndexUpgrader /var/solr/data/hms/data/index/

它无声地运行，所以我的假设是它做了它必须正确做的事情。
然后我升级到solr 8.7.0，并启动了脚本：

/opt/solr/server/solr-webapp/webapp/WEB-INF/lib$ sudo java -cp lucene-core-8.7.0.jar:lucene-backward-codecs-8.7.0.jar org.apache.lucene.index.IndexUpgrader /var/solr/data/hms/data/index/

最后一个代码退出时出现以下错误：

Exception in thread "main" org.apache.lucene.index.IndexFormatTooOldException: Format version is not supported (resource BufferedChecksumIndexInput(MMapIndexInput(path="/var/solr/data/hms/data/index/segments_asky"))): This index was initially created with Lucene 6.x while the current version is 8.7.0 and Lucene only supports reading the current and previous major versions.. This version of Lucene only supports indexes created with release 7.0 and later.
    at org.apache.lucene.index.SegmentInfos.readCommit(SegmentInfos.java:322)
    at org.apache.lucene.index.SegmentInfos.readCommit(SegmentInfos.java:291)
    at org.apache.lucene.index.SegmentInfos$1.doBody(SegmentInfos.java:461)
    at org.apache.lucene.index.SegmentInfos$1.doBody(SegmentInfos.java:458)
    at org.apache.lucene.index.SegmentInfos$FindSegmentsFile.run(SegmentInfos.java:720)
    at org.apache.lucene.index.SegmentInfos$FindSegmentsFile.run(SegmentInfos.java:672)
    at org.apache.lucene.index.SegmentInfos.readLatestCommit(SegmentInfos.java:463)
    at org.apache.lucene.index.DirectoryReader.listCommits(DirectoryReader.java:260)
    at org.apache.lucene.index.IndexUpgrader.upgrade(IndexUpgrader.java:158)
    at org.apache.lucene.index.IndexUpgrader.main(IndexUpgrader.java:78)
    Suppressed: org.apache.lucene.index.CorruptIndexException: checksum passed (58082b0a). possibly transient resource issue, or a Lucene or JVM bug (resource=BufferedChecksumIndexInput(MMapIndexInput(path="/var/solr/data/hms/data/index/segments_asky")))
        at org.apache.lucene.codecs.CodecUtil.checkFooter(CodecUtil.java:466)
        at org.apache.lucene.index.SegmentInfos.readCommit(SegmentInfos.java:434)
        ... 9 more

为什么？我是否做得不对，即先将索引从6升级到7，然后再从7升级到8？如何使我的索引与solr8一起工作？