diff --git a/src/iocore/cache/CacheTest.cc b/src/iocore/cache/CacheTest.cc
index 71b38738e3c..a722fcb0513 100644
--- a/src/iocore/cache/CacheTest.cc
+++ b/src/iocore/cache/CacheTest.cc
@@ -432,9 +432,14 @@ force_link_CacheTest()
 
 REGRESSION_TEST(cache_disk_replacement_stability)(RegressionTest *t, int level, int *pstatus)
 {
-  static int const                                MAX_VOLS            = 26; // maximum values used in any test.
-  static uint64_t                                 DEFAULT_SKIP        = 8192;
-  static uint64_t                                 DEFAULT_STRIPE_SIZE = 1024ULL * 1024 * 1024 * 911; // 911G
+  static int const MAX_VOLS     = 26; // maximum values used in any test.
+  static uint64_t  DEFAULT_SKIP = 8192;
+  // Reduced from 911GB to 1GB for CI stability. The Stripe constructor
+  // allocates a directory buffer proportional to stripe size, and 26 stripes
+  // of 911GB each exhausted memory in CI environments (especially under
+  // Valgrind). The hash stability algorithm works identically regardless of
+  // absolute stripe size.
+  static uint64_t                                 DEFAULT_STRIPE_SIZE = 1024ULL * 1024 * 1024; // 1GB
   CacheDisk                                       disk; // Only need one because it's just checked for failure.
   CacheHostRecord                                 hr1, hr2;
   StripeSM                                       *sample;
@@ -471,7 +476,7 @@ REGRESSION_TEST(cache_disk_replacement_stability)(RegressionTest *t, int level,
   hr2.num_vols       = MAX_VOLS;
 
   sample      = stripes[sample_idx].get();
-  sample->len = 1024ULL * 1024 * 1024 * (1024 + 128); // 1.1 TB
+  sample->len = 1024ULL * 1024 * 1024 + 256ULL * 1024 * 1024; // 1.25GB (proportional increase from 1GB)
   snprintf(buff, sizeof(buff), "/dev/sd%c %" PRIu64 ":%" PRIu64, 'a' + sample_idx, DEFAULT_SKIP, sample->len);
   CryptoContext().hash_immediate(sample->hash_id, buff, strlen(buff));
   build_vol_hash_table(&hr2);
@@ -566,6 +571,7 @@ test_RamCache(RegressionTest *t, RamCache *cache, const char *name, int64_t cach
       CryptoHash    hash;
 
       d->alloc(BUFFER_SIZE_INDEX_16K);
+      memset(d->data(), 0, BUFFER_SIZE_FOR_INDEX(BUFFER_SIZE_INDEX_16K));
       data.push_back(make_ptr(d));
       hash.u64[0] = (static_cast<uint64_t>(i) << 32) + i;
       hash.u64[1] = (static_cast<uint64_t>(i) << 32) + i;
@@ -610,6 +616,7 @@ test_RamCache(RegressionTest *t, RamCache *cache, const char *name, int64_t cach
     if (!cache->get(&hash, &get_data)) {
       IOBufferData *d = THREAD_ALLOC(ioDataAllocator, this_thread());
       d->alloc(BUFFER_SIZE_INDEX_16K);
+      memset(d->data(), 0, d->block_size());
       data.push_back(make_ptr(d));
       cache->put(&hash, data.back().get(), 1 << 15);
       if (i >= sample_size / 2) {
@@ -630,6 +637,7 @@ test_RamCache(RegressionTest *t, RamCache *cache, const char *name, int64_t cach
     if (!cache->get(&hash, &get_data)) {
       IOBufferData *d = THREAD_ALLOC(ioDataAllocator, this_thread());
       d->alloc(BUFFER_SIZE_INDEX_8K + (r[i] % 3));
+      memset(d->data(), 0, d->block_size());
       data.push_back(make_ptr(d));
       cache->put(&hash, data.back().get(), d->block_size());
       if (i >= sample_size / 2) {
diff --git a/src/iocore/cache/Stripe.cc b/src/iocore/cache/Stripe.cc
index ebd98d06429..ace5e5f1bf8 100644
--- a/src/iocore/cache/Stripe.cc
+++ b/src/iocore/cache/Stripe.cc
@@ -164,8 +164,9 @@ Stripe::_init_directory(std::size_t directory_size, int header_size, int footer_
     this->directory.raw_dir_huge = false;
   }
   this->directory.raw_dir_size = directory_size;
-  this->directory.dir          = reinterpret_cast<Dir *>(this->directory.raw_dir + header_size);
-  this->directory.header       = reinterpret_cast<StripeHeaderFooter *>(this->directory.raw_dir);
+  memset(this->directory.raw_dir, 0, directory_size);
+  this->directory.dir    = reinterpret_cast<Dir *>(this->directory.raw_dir + header_size);
+  this->directory.header = reinterpret_cast<StripeHeaderFooter *>(this->directory.raw_dir);
   std::size_t const footer_offset{directory_size - static_cast<std::size_t>(footer_size)};
   this->directory.footer = reinterpret_cast<StripeHeaderFooter *>(this->directory.raw_dir + footer_offset);
 }
diff --git a/src/proxy/logging/LogBuffer.cc b/src/proxy/logging/LogBuffer.cc
index c183bede9e2..eb69c37c1d0 100644
--- a/src/proxy/logging/LogBuffer.cc
+++ b/src/proxy/logging/LogBuffer.cc
@@ -126,6 +126,8 @@ LogBuffer::LogBuffer(const LogConfig *cfg, LogObject *owner, size_t size, size_t
   }
   m_buffer = static_cast<char *>(align_pointer_forward(m_unaligned_buffer, buf_align));
 
+  memset(m_buffer, 0, size);
+
   // add the header
   hdr_size = _add_buffer_header(cfg);